FTM planning first play date

I am planning my first play date and I am not sure what normal protocal is lol. It will be with 2 boys, one is 3 months older, one 3 months younger than my son (17 months). I have known their moms for a while but we are still 'newer' friends if that makes sense. It will be in the later afternoon.

Anyways I'm going to have snacks available for the kids. I am figuring I should gave simple ones for us too. How long do play dates normally last? How many toys should I have out? We cycle them so my son doesn't get bored. I am not sure why I am stressing. These ladies are super nice I just want it to go well and I dont have people over a lot.