Arrival windows are managed under your Company> General settings
Notification Window start - Amount of time Prior to the scheduled start time you want the window to be
Notification Window End - Amount of time After the start time you want your arrivlal window to end at
Please note - if you want it to be before the time, it needs to be a negative number.
Ex: Scheduled time is 1:30 but you want a window of 1-2, you will need to put -30 in the start box, and 30 in the end box.