No, I apologize. my suggestion will not work for you- I did not consider your situation.
You want to define a time window that extends the length of the weekend and for the job to run once during this time frame?
Backup Exec's job window cannot exceed 23:59:59 sec. Extending the window to more than 24hrs makes scheduling tricky- it can cause the same job to run more than once, or for the next day's job to 'miss' .
I imagine you are performing the full backups during this time?
An alternate approach is to define a few policies spanning the time frame. For example- one for Friday night, one for Saturday night, and one for Sunday night and distribute selections lists evenly across them so that all jobs get an opportunity to start within 24 hours.