When should I test?

Sonja

I have 2 <a href="https://play.google.com/store/apps/details?id=com.glow.android">fertility apps</a> and one of of them it said I was supposed to start AF last Thursday december 7th and Glow said I was supposed to get AF on Saturday December 9th. Nothing has happened but I am experiencing cramps, not too terrible but annoying enough to be noticeable.

Is it too early to test? Tests are so expensive...