How comfortable are you that all your parameters are now, and will in the future, be stable?
Check frequently at first and then less frequently as you get comfortable, start out doing it every day, then every other day, then once a week.
I had a friend who was so paranoid about water quality and the potential for something going wrong that he checked his parameters every day for years! On the other hand, I'm pretty comfortable that I have things under control and would probably see an issue if it happened, that I test every month. And that's mostly to make sure my dosing pumps are dosing at the proper levels. As corals and coraline algae develop and get bigger, they use more Ca and alk, so I need to stay in touch with the demand.