diff --git a/docs/scheduler/ci.md b/docs/scheduler/ci.md
index 2640a155..bd3689bb 100644
--- a/docs/scheduler/ci.md
+++ b/docs/scheduler/ci.md
@@ -211,9 +211,17 @@ following to your host config:
 {
   # Daily GC: delete store paths not referenced by a live root and older
   # than a day. Keeps the store bounded between builds.
+  #
+  # `randomizedDelaySec` because a fixed daily time lands on the same wall
+  # clock as whatever else runs nightly. A collection that overlaps a CI
+  # job does not fail it — the runner builds through the host nix-daemon,
+  # so an in-flight build's temp roots are protected — but the first build
+  # after a collection rebuilds what the collection deleted, so a run that
+  # lands just behind one pays for it in wall time.
   nix.gc = {
     automatic = true;
     dates = "daily";
+    randomizedDelaySec = "45min";
     options = "--delete-older-than 1d";
   };
 
@@ -231,6 +239,13 @@ following to your host config:
 store, so the same GC config should be applied wherever the builder runs —
 GC on the coordinator host won't reclaim space on the builder.
 
+⚠️ Two stores also means the temp-root protection above **doesn't span
+them**. Each daemon holds roots only for the builds it runs, so a
+collection on the _builder_ knows nothing about a coordinator build
+waiting on a path there. Stagger the two hosts' GC windows rather than
+giving them the same `dates`, and prefer `min-free`/`max-free` on the
+builder — disk-pressure collection at least runs while nothing is mid-copy.
+
 ## References
 
 - `nix/host-modules/hive-ci.nix`: runner configuration, auto-registration script, container setup.