I post 6 days a week (and once a month on Sundays - like today!). Surprisingly, my numbers seem to go up during the weekend? I've always heard weekend updates were kinda the dead zone. My comic does feature weekly stories that wrap on Saturdays though, so it could be people popping in to catch up on the week. Thursday also seems to do consistently well, for w/e reason, lol.
As for time, I try to keep it consistent during a given week, but I play with different times week-to-week. One week it's 3am (EST), next it'll be 6am, etc. I won't go past noon, just, because! I find I maybe get slightly better results when I post earlier, but I have no idea how Tapas' discoverability works, in that regard.