> Bidding is open as long as there have been bids in the past 5 minutes.
You also have to proportionally raise the bid increment, or you'll have people bidding $1 up at the end of every 5 minute period in order to exhaust and frustrate the person they're bidding against. Their opponent's only choices are 1) to mirror the $1 raises, which could go on for ages (then sleep and automation become issues), or 2) to make a big jump hoping that they jump past their opponents limit.
In the case of 2) the dollar bidder's limit could be +$10, and there's no rational way for their opponent to choose the amount for a big jump other than jumping to their limit. Meaning that they just wipe away all of their potential bargain and get it for their valuation. Leaves a sour taste; feels like they're bidding against themselves.
As somebody who auctions things, I use a required greater than "≈10%" of the current bid amount bid increment, and the auction doesn't end on an item until there hasn't been a bid for 10 minutes. Works great. "≈10%" means to just drop the last digit of the current bid to know the minimum next bid. Then I can set the auction to end an hour before I really want it to end; if it hasn't ended by then it's because I mispriced something and the right people found it.
You capture all the value you can, and it runs completely unattended. You just need a way to timestamp bids and broadcast that timestamp e.g. a forum post.