my DS always needed a wind down time after preschool -lnch and then Tv and some days a visit to the very near and not v exciting park later on was quite enough we fitted in swimming later afternoon sometimes and usually saw friends one after noon but from 2ish onewards
My 3rd is 2.11. He does five mornings and I pick him up a 12.15. Sometimes we do a very quick shop just essentials but invariably we go home and he chills out watching chuggington! Later we go out on the scooter/park/ see a friend/play in the garden etc but nothing too much otherwsie he is hanging by 4pm and tea time becomes hellish! I am lucky, I do not have to do school,my older two are now a secondary. Makes life easier!
My 3 year old has just started nursery too 5 afternoons and I do think it takes it out of them!
If I were you OP, I'd plan for a slump when you get home. Big lunch first if they've not had at nursery (would even consider main meal at this point if you can be bothered even just for a few months as i think they can degenerate as the day progresses and good to have proper meal done so tea can just be a roll/beans on toast/something dead simple and quick).
I'd then factor in up to an hour "slump" and would pop Cbeebies or a DVD on. Then I'd try to get them outside for an hour or 2 if the weather's nice. If you've not got much planned I'd do 4pm bath if necessary, mine always pick up again after bath. I'd bring bedtime forward and if all's going smoothly they can play on until bedtime but if not pop them down at 6.30pm (or whatever).
My issue is that our knackered 3 year old is the youngest and teatime/late afternoon's not always the calmest for her, wee lamb. She has a blanket that she generally just has in bed but it's frequently "needed" by 4pm-ish! And eating her tea is a bit of a battle but I'm going to try to chill about it for a few more weeks and I do think the main issue is that she's exhausted!