Basically 1-1.5 hours every evening, and then at weekends 2-3 hours each day. So I suppose 9-11.5 hours a week.
At times I feel resentful but then feel terribly guilty for feeling that way.
For background, he's out of the house 11 hours a day Mon-Fri (work + commute) and I'm a SAHM.
He literally never has a day off from his hobby, not even on holiday (in fact he spends more time doing it).
The children are in bed by 9pm but then I go to bed at about 10.30pm because I have to be up pretty early. He's a night owl who needs less sleep so sometimes stays up later than me doing his hobby.