It is a fact that items ending on a Sunday evening can sell for up to 50% more than items ending at any other time. This is from personal experience and is also borne out by statistics on selling prices over a 12 month period.

The only time to avoid a Sunday is when Ebay runs a cheap listing day, then everyone and his dog lists items and the selling prices tend to dip.

So the best time to list is on a Thursday evening to finish in 10 days time on a Sunday evening, it gives your item the maximum time exposure and should also get a premium price. Conversly never buy on a Sunday