As you say, in a standard auction you can expect the same equilibrium using second price and a traditional bidding system. The difference is that participants

As you say, in a standard auction you can expect the same equilibrium using second price and a traditional bidding system. The difference is that participants need to waste time rebidding after being outbid and can face a technical challenge of submitting bids in time in the scrambles that inevitably occur just before auctions close. However, as you point out, the situation gets worse because we want to create a queue of low-bidders willing to step in should the original winner fail to deliver. Allowing multiple bids and/or bids higher than the current lowest would go some way to addressing this but participants may bid strategically. Eg the current lowest is $50, I'm willing to do it for $70 but don't expect any more bids under $100 so bid $95, failing to get the job when someone else bids $80. Also it's unclear whether I get 2 x 10 days to complete the task if I bid both the lowest and second lowest bid, which is clearly suboptimal and could even lead to people placing a chain of lower and lower bids, completing a functional solution but then deliberately waiting for their lower bids to time out before submitting the solution. A second price auction would be better in this case for both these reasons.