Does he want to discuss these things when he comes to pick up D4?
If so, pick-ups and drop-offs are not good places to have serious discussions about anything. That is very disruptive to kids. I'd suggest having a phone call or a separate 1:1 if discussions veer into serious territory.
Of course if he just wants to discuss some minor things about D4 and you know what those things are ahead of time, maybe it's okay.
If he wants to discuss the D, saying you would like time to think is completely valid. In fact, I would say even if you thought your H was offering more than a fair compromise, you should *still* say you need more time. You are not on his timeline, this is completely ok.
