Not at a variance level I'm willing to accept. Time is required only when variance falls into a range I'm comfortable with. 0.003 BTC/MH is not an acceptable low end spike for me. It could be considered an outlier, but when two separate tests achieved the same low end spike on two different days it was not worth my effort to try again until other clients start reporting better stability.
If you're not willing to accept variance then you have no business on a 500 MH pool. Just take a look at the pool hash rate and move on (until it gets bigger at least).