late ovulation

je
Been testing all of last week because glow predicted my fertile window was 5/15-5/21 (ovulating Sat)have not yet ovulated been checking everyday with clearblue and keep getting a negative surge.  My question is what times should I test? First thing in the morning now&at 9pm ok?? I am also testing with other OPK strips just in case& I do see the max line on the OPK strips getting darker so im hoping I ovulate soon. Gyno put me on Metformin last month so im praying I get a BFP soon. Period says it's supposed to arrive on July 4th have any of you ladies ovulated this close to your period? Do you think it's normal?