hydra: optimise periodically to speed up jobs

hosts/hydra/default.nix

@@ -39,6 +39,10 @@ in
     daemonCPUSchedPolicy = "idle";
     daemonIOSchedClass = "idle";
     daemonIOSchedPriority = 7;
+    optimise = {
+      automatic = true;
+      dates = [ "05:30" ];
+    };
     remoteBuilder = {
       enable = true;
       sshPublicKeys = config.users.users.root.openssh.authorizedKeys.keys ++ [
@@ -47,7 +51,6 @@ in
     };
     settings = {
       allowed-uris = "http:// https:// ssh://";
-      auto-optimise-store = true;
       builders-use-substitutes = true;
       cores = 20;
       keep-outputs = true;