The stipend covers everything else after a normal school day M-F. That includes all things after school, including a Friday nights and all Saturdays (and even Sunday stuff if it rarely happens).
Your 217 is WAY more valuable, because those 3% raises apply to your daily rate, so you get a bigger bump than normal teacher on a 187 (I know the 187 thing is kinda going away, but still...) Places I have seems that give longer contracts to assistants usually come with a slightly lower stipend, due to the fact that those extra days are so much more valueable.
Iím a head director on a 225, but the rest of the directors are on a 187. I really wish they could go on more like 207 so that the week we clean up after school ends and all the summer band stuff is paid by salary. TBH they likely doing get paid anything for that, as we know how fast stipends are spent...do they even last through marching season?
30 extra days times your daily rate (salary/187) is what you get paid higher than other teachers on a 187, and then compare that to the stipend. The stipend is low, but those 30 days are likely higher than the stipend. When I was an assistant I would have taken extra days in a second, especially because the head director demanded I be there the same days, and the HD got those extra days.
I hope this helps out. There are definitely some pros and cons, but your situation is likely better than a lot of HS assistants.