Glow vs my body

Je
Hi ladies. I'm in my TWW and now sure what to think. Glow says I'm due to get AF on Saturday 4/12 however historically my body almost always has AF show ups on a Tuesday or 4/18.  When it come now to being late what do I do? If AF doesn't come when glow predicts am I late? Or just wait till after 18th to consider being late?
​I'm gonna test on Saturday 4/12 I think
​Thanks!