diff --git a/operating-systems/buer/shepherd-services.scm b/operating-systems/buer/shepherd-services.scm
index a624d10..ab5217d 100644
--- a/operating-systems/buer/shepherd-services.scm
+++ b/operating-systems/buer/shepherd-services.scm
@@ -27,7 +27,9 @@ next calendar event.")))
     (provision '(guix-gc))
     (modules '((shepherd service timer)))
     (start #~(make-timer-constructor
-               (calendar-event #:days-of-month '(1 15))
+               (calendar-event #:days-of-month '(1 15)
+                               #:hours '(8 14 20)
+                               #:minutes '(0))
                (command '("guix" "gc" "--optimize" "--free-space=10G"))))
     (stop #~(make-timer-destructor))
     (actions (list timer-trigger-action))))