diff --git a/index.web.js b/index.web.js
index 4dee831c..96237345 100644
--- a/index.web.js
+++ b/index.web.js
@@ -1,3 +1,5 @@
+import '#/platform/markBundleStartTime'
+
 import '#/platform/polyfills'
 import {registerRootComponent} from 'expo'
 import {doPolyfill} from '#/lib/api/api-polyfill'
diff --git a/src/platform/markBundleStartTime.web.ts b/src/platform/markBundleStartTime.web.ts
new file mode 100644
index 00000000..cd64c9f1
--- /dev/null
+++ b/src/platform/markBundleStartTime.web.ts
@@ -0,0 +1,2 @@
+// @ts-ignore Web-only. On RN, this is set by Metro.
+window.__BUNDLE_START_TIME__ = performance.now()