Also in a year or so he’ll be full time school, and then this job opportunity probably won’t be here. Have to look long term. My sons in nursery 24 hours a week, he used to be in 30 since 10 months old until a friend kindly offered to have him for an afternoon a week. He’s never had any issue, yes it might be an adjustment for a few weeks getting used to be extra tired but he’ll manage and work itself out. I’d say go for the new job, do it for you
The mum guilt doesn't go away but you need to do what's best for your family. If your son is happy then I don't think it makes that much difference to them at this age if it's 2 days or 5.