Happy to be told IABU but thought I'd get some outside perspective.
Ex h has DS 1 day a week that I work but he doesn't. It has recently increased from 5/6 hours to approx 9 hours.
Last time he had DS I was asked to do overtime at work unexpectedly which I agreed to as it still left me just under an hour until ex h bought DS back to me.
I text ex when I finished work and asked if he minded having DS for an extra 30 mins as I had a lot of housework/jobs I wanted to do. He agreed and said no problem will bring him back at x time.
I thought everything was fine but then an hour or so later I get a text from his mum (ex mil) basically stating how unfair she thought it was that ex had had DS all day (8:30-5:30 extended til 6) and that I 'dumped' extra time on him without warning etc.
AIBU in thinking that it's none of her business (he does live with her but I don't think that matters) and even if it was - ex agreed in the first place? Thinking I'll just ignore her 
