Clear blue OPK question

Jordan

I’ve been using the clear blue digital for several cycles now and I usually get 3-4 days with a flashing smiley face and then the peak. My last 2 cycles I went from a negative test to a peak within 24 hours with no flashing smiley. I’ve also been letrozole for the past 3 cycles not sure if that has anything to do with it? Just odd to me.