I would think it is hard to stay at full capacity open only half days. There are often many stay at home mom families that want their child in half day group settings but I suspect they would make use of the many city run preschools versus a small home group that has mixed ages and only a few kids.

I'm not sure what city you are in but Ottawa had MANY really cheap preschool options...like $10 a day (2-2.5hrs) and that jut seems easier and cheaper than paying a home daycare for socialization. I would also be looking for a larger group of same aged children for socialization.

If you only want to work part time and run a home daycare I do think you are best to choose a few days (Tues/Thurs or (Mon/Wed/Fri) and work full days. There are TONS of families where one parent only works a few days a week and even MORE families where grandparents want to take the kids 2 days a week so they don't need 5 days.