Question, need answer
 

Do you have to drop your verse within the set time after BOTH people check in, or just after you check in?

you have to obviously post your verse within time specified. Theres a time limit set up for check in,then another one for posting your verse.

but really though, your opponent can just gain an advantage by waiting until the last minute to check in, so he can have another 3 days to write

Yeah i know, but the limit starts as soon as you check.

its all about timing.