How fast does CM change from non-fertile to fertile?

This morning my CM was creamy, which is non fertile right? A few hours later, I checked again and it was still creamy. An hour later I checked again cause it felt like I peed myself and it was watery... Which is fertile right?? I took an opk this morning and I'm pretty sure it came out positive (not 100% sure cause it's a different test than I took last time I was tracking and these lines are SUPER light).