tweak cron timer

nixos/ghc-perf.nix

@@ -99,7 +99,7 @@ in {
     wants = [ "network.target" ];
     wantedBy = [ "multi-user.target" ];
     timerConfig = {
-      OnCalendar = "*-*-* 8:00:00";
+      OnCalendar = "*-*-* 3:00:00";
       Unit = "ghc-note-perf-import.service";
     };
   };