idk, i had 800 and 1500 spex stake at day 5. so far at the current moment I would say it doesnt matter how large it is, itll still be 5 days.
I would say that the block size will always affect the rate that you stake at. That is the very principle of POS that the bigger the block stakes faster and the smaller ones stake slower. Check out some white papers on Proof of Stake.
The pos difficulty is low right now so you wont notice much disadvantage for small blocks. going forward the pos difficulty will rise and give some advantage to larger blocks and allow them to stake faster. faster staking gives more compounding so big blocks are the best way to go.