diff --git a/scripts/build-date-plugin.js b/scripts/build-date-plugin.js
new file mode 100644
index 00000000..b516871b
--- /dev/null
+++ b/scripts/build-date-plugin.js
@@ -0,0 +1,40 @@
+/**
+ * Vite plugin: writes the date of the build into the card.
+ */
+
+// Strict length requirement: See below.
+export const BUILD_DATE_PLACEHOLDER = '__BUILD_DATE_SENTINEL___';
+
+/**
+ * The date cannot be handed to the bundler as a substituted name, because the
+ * build configuration is evaluated once and `vite build --watch` reuses it.
+ * As such, every rebuild would report the time the watcher started rather than
+ * the actual build time. Output is generated afresh for each build, so the date
+ * is written here instead.
+ *
+ * @type {() => import('vite').Plugin}
+ */
+export const buildDate = () => ({
+  name: 'build-date',
+
+  renderChunk(code) {
+    if (!code.includes(BUILD_DATE_PLACEHOLDER)) {
+      return null;
+    }
+
+    const date = new Date().toISOString();
+    if (date.length !== BUILD_DATE_PLACEHOLDER.length) {
+      this.error(
+        'The build date must be exactly as long as the placeholder it replaces.',
+      );
+    }
+
+    return {
+      code: code.replaceAll(BUILD_DATE_PLACEHOLDER, date),
+
+      // The replacement is exactly as long as what it replaces, so the existing
+      // sourcemap still describes the code.
+      map: null,
+    };
+  },
+});
diff --git a/scripts/build-defines.js b/scripts/build-defines.js
index 71091d55..dd01b06e 100644
--- a/scripts/build-defines.js
+++ b/scripts/build-defines.js
@@ -1,6 +1,8 @@
 import { execFileSync } from 'node:child_process';
 import { readFileSync } from 'node:fs';
 
+import { BUILD_DATE_PLACEHOLDER } from './build-date-plugin.js';
+
 /**
  * Asks git something or gives back nothing when it cannot be asked.
  */
@@ -23,7 +25,11 @@ const getPackageVersion = () =>
  *
  * `releaseVersion` is the version being released, which only the release
  * workflow knows; a build without one reports the version in `package.json`, or
- * a development build the commit it was made from.
+ * a development build the commit it was made from. Its presence is what makes a
+ * build a released one.
+ *
+ * The build date is a placeholder here, written in for by the `buildDate`
+ * plugin as each build's output is generated.
  *
  * The values are JSON so that a bundler can drop them in as written.
  */
@@ -35,10 +41,11 @@ export const getBuildDefines = ({ dev, releaseVersion }) => {
     __ADVANCED_CAMERA_CARD_RELEASE_VERSION__: JSON.stringify(
       releaseVersion ?? (dev ? developmentVersion : getPackageVersion()),
     ),
+    __ADVANCED_CAMERA_CARD_IS_RELEASE_BUILD__: JSON.stringify(!!releaseVersion),
     __ADVANCED_CAMERA_CARD_GIT_HASH__: JSON.stringify(gitHash),
     __ADVANCED_CAMERA_CARD_GIT_DATE__: JSON.stringify(
       askGit('log', '-1', '--format=%cI'),
     ),
-    __ADVANCED_CAMERA_CARD_BUILD_DATE__: JSON.stringify(new Date().toISOString()),
+    __ADVANCED_CAMERA_CARD_BUILD_DATE__: JSON.stringify(BUILD_DATE_PLACEHOLDER),
   };
 };
diff --git a/src/components/loading.ts b/src/components/loading.ts
index f9d76681..30aa811d 100644
--- a/src/components/loading.ts
+++ b/src/components/loading.ts
@@ -9,7 +9,8 @@ import { customElement, property } from 'lit/decorators.js';
 
 import loadingStyle from '../scss/loading.scss?inline';
 import type { EffectName, EffectsManagerInterface } from '../types';
-import { getReleaseVersion } from '../utils/build-info.js';
+import { formatDateAndTime } from '../utils/basic.js';
+import { getReleaseVersion, getUnreleasedBuildDate } from '../utils/build-info.js';
 
 import './icon';
 
@@ -80,10 +81,14 @@ export class AdvancedCameraCardLoading extends LitElement {
   }
 
   protected render(): TemplateResult {
+    const buildDate = getUnreleasedBuildDate();
+
     return html`<advanced-camera-card-icon
         .icon=${{ icon: 'advanced-camera-card:iris' }}
       ></advanced-camera-card-icon
-      ><span>${getReleaseVersion()}</span>`;
+      ><span>${getReleaseVersion()}</span> ${buildDate
+        ? html`<span class="build-date">${formatDateAndTime(buildDate, true)}</span>`
+        : ''}`;
   }
 
   static get styles(): CSSResultGroup {
diff --git a/src/scss/loading.scss b/src/scss/loading.scss
index d1077f50..5ff3e7be 100644
--- a/src/scss/loading.scss
+++ b/src/scss/loading.scss
@@ -53,3 +53,8 @@ advanced-camera-card-icon {
 span {
   font-size: x-large;
 }
+
+.build-date {
+  font-size: medium;
+  opacity: 0.7;
+}
diff --git a/src/utils/build-info.ts b/src/utils/build-info.ts
index 92eb6067..5794721a 100644
--- a/src/utils/build-info.ts
+++ b/src/utils/build-info.ts
@@ -1,4 +1,5 @@
 declare const __ADVANCED_CAMERA_CARD_RELEASE_VERSION__: string | undefined;
+declare const __ADVANCED_CAMERA_CARD_IS_RELEASE_BUILD__: boolean | undefined;
 declare const __ADVANCED_CAMERA_CARD_GIT_HASH__: string | undefined;
 declare const __ADVANCED_CAMERA_CARD_GIT_DATE__: string | undefined;
 declare const __ADVANCED_CAMERA_CARD_BUILD_DATE__: string | undefined;
@@ -25,6 +26,14 @@ const BUILD_DATE =
   typeof __ADVANCED_CAMERA_CARD_BUILD_DATE__ === 'undefined'
     ? undefined
     : __ADVANCED_CAMERA_CARD_BUILD_DATE__;
+
+const IS_RELEASE_BUILD =
+  typeof __ADVANCED_CAMERA_CARD_IS_RELEASE_BUILD__ === 'undefined'
+    ? false
+    : __ADVANCED_CAMERA_CARD_IS_RELEASE_BUILD__;
+
+const UNRELEASED_BUILD_DATE =
+  !IS_RELEASE_BUILD && BUILD_DATE ? new Date(BUILD_DATE) : null;
 /* v8 ignore stop -- @preserve */
 
 export interface GitInfo {
@@ -34,6 +43,8 @@ export interface GitInfo {
 }
 
 export const getReleaseVersion = (): string => RELEASE_VERSION;
+export const getUnreleasedBuildDate = (): Date | null => UNRELEASED_BUILD_DATE;
+
 export const getGitInfo = (): GitInfo => ({
   hash: GIT_HASH,
   commitDate: GIT_DATE,
diff --git a/tests/utils/build-info.test.ts b/tests/utils/build-info.test.ts
index 3d258fc9..13fae50d 100644
--- a/tests/utils/build-info.test.ts
+++ b/tests/utils/build-info.test.ts
@@ -1,6 +1,10 @@
 import { describe, expect, it } from 'vitest';
 
-import { getGitInfo, getReleaseVersion } from '../../src/utils/build-info';
+import {
+  getGitInfo,
+  getReleaseVersion,
+  getUnreleasedBuildDate,
+} from '../../src/utils/build-info';
 
 // As these are running as tests, the won't be build substitutes so this only
 // tests default/fallback values.
@@ -16,3 +20,9 @@ describe('getGitInfo', () => {
     expect(getGitInfo()).toEqual({});
   });
 });
+
+describe('getUnreleasedBuildDate', () => {
+  it('should report no build date for an unbuilt card', () => {
+    expect(getUnreleasedBuildDate()).toBeNull();
+  });
+});
diff --git a/vite.config.ts b/vite.config.ts
index a6757582..1afbf6a0 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -1,6 +1,7 @@
 import { visualizer } from 'rollup-plugin-visualizer';
 import { defineConfig } from 'vite';
 
+import { buildDate } from './scripts/build-date-plugin.js';
 import { getBuildDefines } from './scripts/build-defines.js';
 import { cleanDist } from './scripts/clean-dist-plugin.js';
 import { facadeEntry } from './scripts/facade-entry-plugin.js';
@@ -24,6 +25,7 @@ export default defineConfig(({ mode }) => {
     plugins: [
       cleanDist(),
       svgPath(),
+      buildDate(),
       facadeEntry({ publicFileNames: PUBLIC_ENTRIES }),
       visualizer({ filename: 'visualizations/treemap.html', template: 'treemap' }),
     ],