Can I test?

Im so confused lol because Glow always predicts my period to be one day after my period actually shows up lol. My cycle is 27 days long. The day after CD27 is when I get my period. Not sure if I should call that CD28/CD1. Anyway lol I’m on CD23 now. Is it too early for me to test? I’m on a family vacation and likely won’t be able to test until tomorrow or Tuesday lol. Just curious if anyone has gotten a positive basically 4-5 days before their period is supposed to start. With my last pregnancy, I tested the day I missed my cycle lol.