“converted” isn’t the right term here. You are always on long call unless “assigned” a SC or FSB.

Notification time minimums (pilots may waive these minimums):

o Trip assignments – 13 hours prior to scheduled departure time
o FSB – 12 hours prior to report time
o SC – 10 hours prior to the start time of the SC assignment. If the assignment is given between 1800-2359, then 12 hour notice is required. (20-K-6-d)