One person in our party has autism and had a GAC with a "Use Alternate Entrance when Available" stamp. Thought it might be helpful to share our experience.
You take your GAC to the Lube O Rama and a CM will give you one FP for the whole party. The return time depended on what time of the day you went. If you showed up right at rope drop, they will give you a FP that lets you return in a hour (at which time the FP line is generally pretty short). If you went later in the day, your return time will be around 3 hours later (maybe so that it's the same as the standby line). I noticed that the FP return line got pretty long at certain points during the afternoon and evening. After they give you the FP, they write a sequence of numbers on your GAC with the date, return time, ride and the CM's initials (I think). When we got off the ride the first time, we were able to obtain a second FP by going to Lube O Rama again. We were conscientious about the long standby line for guests who haven't ridden it once so we didn't go again. But as far as I could tell, you could get a new FP as soon as the previous one had lapsed.
You take your GAC to the Lube O Rama and a CM will give you one FP for the whole party. The return time depended on what time of the day you went. If you showed up right at rope drop, they will give you a FP that lets you return in a hour (at which time the FP line is generally pretty short). If you went later in the day, your return time will be around 3 hours later (maybe so that it's the same as the standby line). I noticed that the FP return line got pretty long at certain points during the afternoon and evening. After they give you the FP, they write a sequence of numbers on your GAC with the date, return time, ride and the CM's initials (I think). When we got off the ride the first time, we were able to obtain a second FP by going to Lube O Rama again. We were conscientious about the long standby line for guests who haven't ridden it once so we didn't go again. But as far as I could tell, you could get a new FP as soon as the previous one had lapsed.