Are OPKs supposed to get gradually darker?

Cassie • Mama of 3 👧🏻🧒🏼👶🏻
I've been using them for 5 days, and there is a faint line, which I know is negative. But they aren't getting darker in the slightest, or lighter. Just the same. It's my first time using them. Did I maybe miss my ovulation? Or should I just keep waiting??