I remember reading on an ebay board that listing on Sunday for 7 days was the best. I used to list on Saturday and have noticed that Sunday works the best!
Remember that Ebay is on Pacific time, so if you are listing in New York, you need to account for the 3 hours. Don't have an auction end at 9:00am est when it is 6:00 am Pacific, no one will be up and bidding.
Often times, the last 1/2 is when you get the most bids.
Also, remember sometimes after you list, the auction is not uploaded to the search option for a few hours. You can see the auction when doing a search of your items listed, but not on the regular search engine. So, don't do it too late in the day, because you will be missing out too!
I find that 3:00pm NY time is best, as it is noon in California and people should be up, even if they slept in on their Sunday!
Good Luck!