2 hours.
Or, if like me, I actually SAY what time the play-date is over.... if at my house. Because, my kids nap.
Or, while in the play-date, and its been almost 2 hours, I will say to "everyone" .... "Okay kids, time to start putting away... have to go soon...."
3-4 hours is a looooonnnnng time for a play-date.
You also have to gauge the cues of the Mom... if she seems petered out already, then graciously pick up on those hints... and leave. Thanking her etc. Or bring over some snacks too.... out of hospitality and since you are the "guest." That is what we always do.... bringing some snack over to the host's house too. Even if not asked.
Usually for me, our playdates are in the morning. Because I have a "schedule" for MY kids too... and they nap as I said. So I don't veer from that.
How old is your kid? Go according to HIS nap time too, if he/you have that routine. After play-dates, it is harder to wind-down the kids... because they have been so active. So allow for that timing...
Since that play-date is at 1:00.... make sure you gauge how long you stay ALSO according to "when" she has to start making dinner for her family too. So don't over-stay in that way....
I've had a few play-dates that lasted 4-5 hours! But that was with good friends/parents that we ALL hang out at my house. But still, its tiring!
good luck,
Susan