Your next decision is how long you want your auction to continue. On eBay, for example, auctions can run three, five, seven or ten days. Most of them last a week.
One thing I can personally attest to, however, is the importance of the time of day. I live in the Eastern time zone, and I submit my auctions around 9 P.M., my time. By this point, most folks on the West Coast are home from work. With my 9 P.M. submission, I can effectively “reach” both sides of the country.
If you have a hot item, and there is any sniping, it will occur near the end of the auction. You want the biggest possible audience for that event.