diff --git a/ui/src/Components/SilenceModal/DateTimeSelect/index.test.js b/ui/src/Components/SilenceModal/DateTimeSelect/index.test.js
index 030b41091..878512442 100644
--- a/ui/src/Components/SilenceModal/DateTimeSelect/index.test.js
+++ b/ui/src/Components/SilenceModal/DateTimeSelect/index.test.js
@@ -1,25 +1,218 @@
 import React from "react";
 
-import { mount } from "enzyme";
+import { mount, shallow } from "enzyme";
+
+import moment from "moment";
 
 import { SilenceFormStore } from "Stores/SilenceFormStore";
-import { DateTimeSelect } from ".";
+import {
+  DateTimeSelect,
+  TabContentStart,
+  TabContentEnd,
+  TabContentDuration
+} from ".";
 
 let silenceFormStore;
 
 beforeEach(() => {
   silenceFormStore = new SilenceFormStore();
+  silenceFormStore.data.startsAt = moment([2060, 1, 1, 0, 0, 0]);
+  silenceFormStore.data.endsAt = moment([2061, 1, 1, 0, 0, 0]);
 });
 
+const ShallowDateTimeSelect = () => {
+  return shallow(<DateTimeSelect silenceFormStore={silenceFormStore} />);
+};
+
 const MountedDateTimeSelect = () => {
   return mount(<DateTimeSelect silenceFormStore={silenceFormStore} />);
 };
 
 describe("<DateTimeSelect />", () => {
+  it("renders 3 tabs", () => {
+    const tree = ShallowDateTimeSelect();
+    const tabs = tree.find("Tab");
+    expect(tabs).toHaveLength(3);
+  });
+
   it("renders 'Duration' tab by default", () => {
     const tree = MountedDateTimeSelect();
     const tab = tree.find(".nav-link.active");
     expect(tab).toHaveLength(1);
+    // check tab title
     expect(tab.text()).toMatch(/Duration/);
+    // check tab content
+    expect(tree.find(".tab-content").text()).toBe("366days0hours0minutes");
+  });
+
+  it("clicking on the 'Starts' tab switches content to 'startsAt' selection", () => {
+    const tree = MountedDateTimeSelect();
+    const tab = tree.find(".nav-link").at(0);
+    expect(tab.text()).toMatch(/Starts/);
+    tab.simulate("click");
+    expect(tree.find(".tab-content").text()).toMatch(/2060/);
+  });
+
+  it("clicking on the 'Ends' tab switches content to 'endsAt' selection", () => {
+    const tree = MountedDateTimeSelect();
+    const tab = tree.find(".nav-link").at(1);
+    expect(tab.text()).toMatch(/Ends/);
+    tab.simulate("click");
+    expect(tree.find(".tab-content").text()).toMatch(/2061/);
+  });
+
+  it("clicking on the 'Duration' tabs switches content to duration selection", () => {
+    const tree = MountedDateTimeSelect();
+    // first switch to 'Starts'
+    tree
+      .find(".nav-link")
+      .at(0)
+      .simulate("click");
+    // then switch back to 'Duration'
+    const tab = tree.find(".nav-link").at(2);
+    expect(tab.text()).toMatch(/Duration/);
+    tab.simulate("click");
+    expect(tree.find(".tab-content").text()).toBe("366days0hours0minutes");
+  });
+});
+
+const ValidateTimeButton = (
+  tab,
+  storeKey,
+  elemIndex,
+  iconMatch,
+  expectedDiff
+) => {
+  const button = tab.find("td > span").at(elemIndex);
+  expect(button.html()).toMatch(iconMatch);
+
+  const oldTimeValue = moment(silenceFormStore.data[storeKey]);
+  button.simulate("click");
+  expect(silenceFormStore.data[storeKey].toISOString()).not.toBe(
+    oldTimeValue.toISOString()
+  );
+  const diffMS = silenceFormStore.data[storeKey].diff(oldTimeValue);
+  expect(diffMS).toBe(expectedDiff);
+};
+
+const ShallowTabContentStart = () => {
+  return shallow(<TabContentStart silenceFormStore={silenceFormStore} />);
+};
+
+const MountedTabContentStart = () => {
+  return mount(<TabContentStart silenceFormStore={silenceFormStore} />);
+};
+
+describe("<TabContentStart />", () => {
+  it("selecting date on DatePicker updates startsAt", () => {
+    const tree = ShallowTabContentStart();
+    const picker = tree.find("DatePicker");
+    const startsAt = moment([2063, 10, 10, 0, 1, 2]);
+    picker.simulate("change", startsAt);
+    expect(silenceFormStore.data.startsAt.toISOString()).toBe(
+      startsAt.toISOString()
+    );
+  });
+
+  it("clicking on the hour inc button adds 1h to startsAt", () => {
+    const tree = MountedTabContentStart();
+    ValidateTimeButton(tree, "startsAt", 0, /angle-up/, 3600 * 1000);
+  });
+
+  it("clicking on the minute inc button adds 1m to startsAt", () => {
+    const tree = MountedTabContentStart();
+    ValidateTimeButton(tree, "startsAt", 1, /angle-up/, 60 * 1000);
+  });
+
+  it("clicking on the hour dec button subtracts 1h from startsAt", () => {
+    const tree = MountedTabContentStart();
+    ValidateTimeButton(tree, "startsAt", 2, /angle-down/, -1 * 3600 * 1000);
+  });
+
+  it("clicking on the minute dec button subtracts 1m from startsAt", () => {
+    const tree = MountedTabContentStart();
+    ValidateTimeButton(tree, "startsAt", 3, /angle-down/, -1 * 60 * 1000);
+  });
+});
+
+const ShallowTabContentEnd = () => {
+  return shallow(<TabContentEnd silenceFormStore={silenceFormStore} />);
+};
+
+const MountedTabContentEnd = () => {
+  return mount(<TabContentEnd silenceFormStore={silenceFormStore} />);
+};
+
+describe("<TabContentEnd />", () => {
+  it("Selecting date on DatePicker updates endsAt", () => {
+    const tree = ShallowTabContentEnd();
+    const picker = tree.find("DatePicker");
+    const endsAt = moment([2063, 11, 5, 1, 3, 2]);
+    picker.simulate("change", endsAt);
+    expect(silenceFormStore.data.endsAt.toISOString()).toBe(
+      endsAt.toISOString()
+    );
+  });
+
+  it("clicking on the hour inc button adds 1h to endsAt", () => {
+    const tree = MountedTabContentEnd();
+    ValidateTimeButton(tree, "endsAt", 0, /angle-up/, 3600 * 1000);
+  });
+
+  it("clicking on the minute inc button adds 1m to endsAt", () => {
+    const tree = MountedTabContentEnd();
+    ValidateTimeButton(tree, "endsAt", 1, /angle-up/, 60 * 1000);
+  });
+
+  it("clicking on the hour dec button subtracts 1h from endsAt", () => {
+    const tree = MountedTabContentEnd();
+    ValidateTimeButton(tree, "endsAt", 2, /angle-down/, -1 * 3600 * 1000);
+  });
+
+  it("clicking on the minute dec button subtracts 1m from endsAt", () => {
+    const tree = MountedTabContentEnd();
+    ValidateTimeButton(tree, "endsAt", 3, /angle-down/, -1 * 60 * 1000);
+  });
+});
+
+const ValidateDurationButton = (elemIndex, iconMatch, expectedDiff) => {
+  const tree = mount(
+    <TabContentDuration silenceFormStore={silenceFormStore} />
+  );
+  const button = tree.find("td > span").at(elemIndex);
+  expect(button.html()).toMatch(iconMatch);
+
+  const oldEndsAt = moment(silenceFormStore.data.endsAt);
+  button.simulate("click");
+  expect(silenceFormStore.data.endsAt.toISOString()).not.toBe(
+    oldEndsAt.toISOString()
+  );
+  const diffMS = silenceFormStore.data.endsAt.diff(oldEndsAt);
+  expect(diffMS).toBe(expectedDiff);
+};
+
+describe("<TabContentDuration />", () => {
+  it("clicking on the day inc button adds 1d to endsAt", () => {
+    ValidateDurationButton(0, /angle-up/, 24 * 3600 * 1000);
+  });
+
+  it("clicking on the day dec button subtracts 1d from endsAt", () => {
+    ValidateDurationButton(2, /angle-down/, -1 * 24 * 3600 * 1000);
+  });
+
+  it("clicking on the hour inc button adds 1h to endsAt", () => {
+    ValidateDurationButton(3, /angle-up/, 3600 * 1000);
+  });
+
+  it("clicking on the hour dec button subtracts 1h from endsAt", () => {
+    ValidateDurationButton(5, /angle-down/, -1 * 3600 * 1000);
+  });
+
+  it("clicking on the minute inc button adds 5m to endsAt", () => {
+    ValidateDurationButton(6, /angle-up/, 5 * 60 * 1000);
+  });
+
+  it("clicking on the minute dec button subtracts 5m from endsAt", () => {
+    ValidateDurationButton(8, /angle-down/, -1 * 5 * 60 * 1000);
   });
 });