Clearblue Advanced Digital OPK

When is it best to test for ovulation? I've always been told noon-5 PM. I use Clearblue Advanced Digital, and got a flashing smiley face (high fertility) Saturday, Sunday, and Monday. The insert mentioned using FMU, so I did that this morning (Tuesday), and got the "low fertility" symbol. Should I test again this afternoon at the same time I have been the last few days?