I would say that I wouldn't spend more than 2 hours, but that doesn't include time when we are actually doing activities at the same time... ie he is helping me cook, garden etc. I would sit down with both boys on the rug & kind of play with them simultaniously eg helping Aiden with a puzzle, while building towers for Liam to distroy, but as a general rule I do lots of things with them "next to me" but not actually actively engaging 1 on 1.
When Liam was a baby, I used to read to Aiden while I fed/settled him for naps & he had a basket of toys in Liam's room to play with whil I did nappy changes. The way they now nap 1 on 1 time is fairly limited & me actually physically playing with them is about 10-15mins every hour... as long as I am right with them I tend to find they play fairly independantly... Liam (unless he is tired or sick) has always been better at it though (Angel vs Spirited/Grumpy), But Aiden isn't too bad especially with out doors play.