I"m not sure the work argument discounts Sunday evening as a valid option though? Surely a counter-argument can be used to say that because most people work Monday-Friday, then Saturday night is the only night they can do things with their family, friends (not that I know what they are), and carry out other social commitments.
I"m a sad git, so I can play many of the Saturday tournaments. However, I have missed a few due to "unavoidable" events - such as weddings and the like.
If you "go" anywhere at a weekend, that makes Saturday night difficult - if not impossible. Anyone who works Mon-Fri will usually have to be back home for Sunday evening - and this seems to me to be the ideal time for an online poker tournament. As has been pointed out elsewhere, many other tournaments are played on a Sunday night. I guess start might have to be slightly earlier than 8 - maybe 7 or even 6 could be feasible?
It might be that one night suits a substantial number, and another night is better for a different group - again consisting of a large number of members. Surely the ideal solution is one that tries to accommodate as many members as possible - and this would suggest to me that the tournaments would need to be held on different days - maybe alternating between Saturday and Sunday?
As KVNSTV pointed out, having the tournaments on different nights might actually help to save a few marriages!