Late Period ,, Best time to take HPT ?? PLEASE HELP

I was supposed to have my period on the 5th , I am 4 days late as of today and the last month I've been feeling so groggy . I have a doctor's appointment tomorrow , but I am so anxious to take a HPT before then . when is the best time that I should take it ? I've read the instructions but I've also read different things from ladies on this forum and I would like some different insight