If you have a mother's helper or part time baby sitter, what do they do? What do you do while they are there? How did you find them?

I SAH with my 2.5 yo and 3 month old. I'm losing my mind some days (most days) with the constant demands on me. The older one does a 2 hour drop off class at the gym once a week and that's it. DH works fairly long hours (like he is rarely home before 7 but usually home by 8).

I'm trying to figure out a short term solution to help me stay sane. The toddler is in a big mommy phase and throws tantrums when DH tries to do things like give her a bath or change her diaper, although she's finally gotten back to a point where she will do fun things with him at least. I'm wondering if getting a babysitter or something a few hours a week would help and how that works.