I think opinions are split on this recalling a few previous threads which you might like to track down. I am of the 'Sunday evening is best' school of thought. I have no real empirical evidence for that though simply generalising from my own activity on Ebay. I tend to schedule things to end on a Sunday around 6 or 7 p.m. but whether that is worthwhile or not, I don't know!
Actually, it is coming back to me now. . .I think someone posted some kind of link showing typical 'transaction traffic' on Ebay, but unhelpfully, I can't remember who, when or where. Sorry! A search would probably bring it up though and/or maybe that member will read this and repost it . . .Here's hoping for you.