I've always used the 0 filter and the 5 filter.

I start by doing a test strip using the 0 filter, on a full sheet of paper.

After deciding the time using the 0 filter, I expose an entire sheet using the 0 filter.

BEFORE removing the paper, I put the 5 filter in and do a test strip.

This results in the time for both the 0 and the 5. I've found that the 5 filter is usually 50% of the 0 time.