To keep his/her job, your Sim has to work at least every other day. If your Sim misses work two days in a row, he/she will be fired.
On the other hand, if you pursue an alternate career, your Sim can work as much or as little as you like. Alternate careers (depending on what expansions you own) include:
- Gardening and selling the vegetables.
- Churning butter
- Sculpting/carving garden gnomes or gargoyles
With any of these, you can set your own hours, though some are more difficult than others. Making gnomes or gargoyles pays very well, potentially netting you 2000 simoleans or more per day, whereas with painting you'll be lucky to clear just shy of 500 per day.