Front of s2 would be something like 5:10-5:15am or so (assuming on time start). So you potentially get an extra 45-50 min of time on course in addition to the 16 min/mile. So in total about 145 min or so (just under 2.5 hrs).
At Princess 5k, I stopped for the first character stop (Merida, Pocohontas, and Moana) and it took us 48 min. The next few characters were either gone or the line was closed. The next line we hit Joy/Sadness was about 4 min based on my Garmin. There were about 10-15 people in that line maybe. Maybe mentally count the number of people in line. Something like a rate of 2-3 people per minute, and use that as a gauge for stopping. It wouldn't surprise me to hear that the Merida line I was in was 100-150 people long by the time I joined.
In front of us at 6:18am (10 min before photo with Merida):
View attachment 652042
Behind us at 6:18am (after standing in this line for 37 min):
View attachment 652037
The lines that we passed that were closed but visible mostly had 15-20 people in them (5-10 min wait). So if you assume you are in 70 min 10k shape (in between stops), then you have about 75 min to stop for photos with an absolute maximization of time on course. Looks like the Princess 10k had about 10 stops, so you can average about 7 min per stop. So if the line is 15-20 people long, then you're good. If it's longer, then you may have to sacrifice time at another stop.