Depending on what you're scripting your prescheduled command in, you can
include a loop that checks the databases every 10 seconds.  Something
like....

dbstop
while (are databases that aren't completely stopped?) {
     sleep 10
}

Then when the while loop exists, your backups will start.

Alex Paschal
Storage Administrator
Freightliner, LLC
(503) 745-6850 phone/vmail