Most mornings half an hour to an hour - he works nights and DS has started waking up just when he comes home, so he does his breakfast and I wake up slowly.
Then just as and when needed - if I want to go out, or go to the shop, or am making dinner. He will quite often step in if I'm getting stressed or if DS isn't listening or just if I'm tired or something. He's with him right now because he's being a pain to put to bed tonight and DP was going for a lie down before work so I've persuaded him to "Go and have a cuddle with and I'll get you some milk" - fingers crossed he hasn't made a sound in 15 minutes!
When we're both at home and awake we are both on duty, I tend to do more nappy changing and cuddling and toothbrushing and things like that, mainly because DP isn't his father and hasn't been around for all his life, and DP is usually sleeping for most of the day, so I'm in charge then, but when he's around we do about an equal amount of playing, getting dressed, getting drinks, food, setting up toys for him, tidying up after him, things like that. DP is more physical in playing and does tickling and wrestling and throwing around and chasing and silly noises and I tend to do more of the imaginative play or drawing or setting up his happyland or helping with a jigsaw or taking him out to see friends, to groups, etc. I do bedtimes, again because I always have done and DS tends to want me. He comes to me if he is hurt.
DS might not be DP's son but he treats him as if he is - it's lovely. With XP I only ever got time to myself when I arranged to go out which probably was once every 6 months! Or when I was making dinner. The rest of the time I was always in charge of DS. Had to fight him to change his own child's nappies FFS! I think it's awful that so many men don't get involved.