pmset wake ignores minutes settings

I am trying to schedule a Crontab job for, say, Monday at 12:59, even when my Mac is sleeping. To achieve this I use pmset repeat wake M 12:58:55 to wake up my Mac 5 seconds before the job. The first problem I encounter is that it is awakened (at the login screen) at 12:58:00 instead of 12:58:55. Since the login screen time before is goes to sleep again is 30 seconds, by 12:59:00 my Mac is already sleeping again, so my job never runs. Is there a way to start the job at the desired time and/or extend the time before my Mac goes back to sleep at the login screen? Currently is set to 30 seconds.