Delay SERVER startup

urBackup is installed in Debian linux.

I want to delay the start of the urBackup server service (or disable autostart and let me start it manually when i need it). How can i achieve it?
I searched the forums and google, but all issues are about delaying clients and not server.

urBackup is backing up into external drive which is not mounted by fstab, so urbackup starts first and finds no drive, starts generating errors.
I cannot use fstab, and this drive is mounted by a custom script.
I want to first mount the drive and then let urbackup start.

thank you