Quoting Katie & Clay's Mommy!:" I've heard a lot of different things. I've used FMU with opks and my results have been pretty accurate. ... [snip!] ... are wacky this month I guess. I'm also twinging on my right side. But if it says to on the box then I suggest go with that."
yeah i just decided to do fmu and then do another one later in the afternoon to be sure. and so far both results each day have been the same. although, the afternoon one was just a little lighter a few times. I finally got a negative today after 4 days in a row of positive opk and the one today was just barely negative. good luck to you ttc!