I aggree with the 48-72 after last bid aucitons, however since the price of bitcoin changes a lot and some of those types of auctions can go on for weeks people might "cancel" their bids if there was a price spike. Maybe I will try it for an experiment here once.
Personally, I think rather than the 48-72 hours 15 minutes is fine. It's called "extended bidding." As long as you placed a big during the regular auction time, you're allowed to place bids after the auction end time. Auction only ends after 15 minutes with no bids. This is how many collectible auction houses run auctions.