For OPUS: If you are using an RTKLib based converter (like Emlid Studio), highly recommend checking the RINEX to see if all timestamps are aligned to whole seconds. If memory serves, OPUS requires every timestamp to be zero aligned to the whole second, so instead of 45.000243, must be 45.000000.
There is some good info in this previous forum thread as well:
OPUS Post processing - GPS/GNSS / Development Boards - SparkFun Community