At 600 hands per hour it would take that long to play them regardless of whether this is a small fraction of the total hands. The rate per hour would be wrong

At 600 hands per hour it would take that long to play them regardless of whether this is a small fraction of the total hands. The rate per hour would be wrong if these are hands where he won less than usual, but in that case he's making a profound (but common) data science mistake by drawing conclusions from a biased sample.