Part-time jobs that fit around childcare - any advice?

I am looking for part-time work that fits around school hours and found a few evening shifts near Sacramento. I am in Sacramento, in case local advice matters. Shifts are four to six hours and the pay is weekly. Is the schedule really fixed?

Thanks for writing this out. I went through something close to it last year, and it settled down once I kept a simple log of every call and form.