Negative OPK late morning. Do I try later?

Emily
Based off Glow and my own estimation, I should be getting a positive OPK today. I tested about 11:45 this morning, admittedly with a less than optimum sample, and got a negative. Was that still too early? Could I get a positive later this afternoon? I've tested every day for the last several days and it's been negative, so I don't think I missed it.