diff --git a/nixos/cachevm/default.nix b/nixos/cachevm/default.nix
index a69eeab..7a4c1f0 100644
--- a/nixos/cachevm/default.nix
+++ b/nixos/cachevm/default.nix
@@ -79,9 +79,10 @@ in
     8080
   ];
 
-  # auto-update cachevm on a separate schedule so that it doesn't clash with
-  # machines that use the cache for their auto-updates.
-  system.autoUpgrade.dates = lib.mkForce "Sun 06:00";
+  # Keep cachevm upgrades on a separate schedule so they don't clash with
+  # machines that use this cache for their own auto-updates.
+  # Run inside the global reboot window (01:00-05:00).
+  system.autoUpgrade.dates = lib.mkForce "Sun 01:00";
 
   systemd.services.atticd.unitConfig.RequiresMountsFor = "/cache";
 }
diff --git a/nixos/default.nix b/nixos/default.nix
index 8d71b85..8180e7e 100644
--- a/nixos/default.nix
+++ b/nixos/default.nix
@@ -78,6 +78,11 @@ in
     dates = lib.mkDefault "Sat 03:00";
     randomizedDelaySec = "45min";
     persistent = true;
+    allowReboot = true;
+    rebootWindow = {
+      lower = "01:00";
+      upper = "05:00";
+    };
   };
 
   time.timeZone = "America/New_York";