Clearblue vs pregmate

Hi guys! Just wanted to reach out and see if anyone could answer this question or give me some insight. The pregmate brand (and pretty much every other opk sticks) says you should test later in the morning or afternoon compared to first morning urine. I just bought Clearblue digital and it says to use first morning urine. Any ideas as to why this would be different? Also when you get a positive opk, when is the best time to have sex? In the morning or evening? Thank you in advance for any responses 🤗