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 blocksize he have mentioned will stake dependend on luck after the 5 days. Later on its much more importend to have big blocks when competition is higher. That means that his 800 coin block can stake faster now than a 10k because of luck. And if he makes a 10k block he will lose coinage so it can be even worse. Its all in white papper and in real use.
So use coincontrol but not if you are sure that it will stake after 5 days because you lose coinage every time and the block starts over again to mature.