Hey Laura,
Sorry the background is escaping me, but I would do as you planned, if you get 2.5 hrs on a Friday, its not like you are palming him off to sit in a SPA (although that would be perfect
), you will probably be cleaning the house, cooking etc and will get that time back from the weekend or the evenings IYKWIM, so I'd stay stick to your plan.
And if your mum repeats her ideas I would explain why you are doing what you are, and if she feels otherwise mayeb she could help withs oem household chores like cooking, shopping and/or cleaning..will tahat go down ok?