Don't worry about the temp of ur urine, that's total overkill. It will naturally be warm of course, and that's fine.
I use fmu for my opks cos that is what fits my daily schedule. A lot of women find their results are not as effective with fmu though, and find clearer results around 2pm or 7pm. If you're going to test afternoons, make sure you abstain from food or drink in the two hours prior, otherwise you'll dilute your result