Nope - you can't *exclude* a time, you can only include it.
If you're brave, though, you can edit the script and reverse the behavior. If you make a copy of the script and save it to "Alert Condition - Scheduled (reverse logic).ppx" (or something similar), you just have to edit one line of the script to change the behavior.
Line 115 of the script is this:
if ((Time < StartTimes(CurDayOfWeek) / (24 * 60))) or (Time >= ((EndTimes(CurDayOfWeek) + 1) / (24 * 60))) then
' We're outside the time window!
If you change it to this, then the time window will be an exclusion window, rather than inclusive:
if ((Time >= StartTimes(CurDayOfWeek) / (24 * 60))) and (Time < ((EndTimes(CurDayOfWeek)) / (24 * 60))) then
' We're inside the time window - don't check!