If the thread is created and you have no bidders (so effectively the auction has not started), you could ask one of the Moderators if they would agree to make the change for you. Once an auction has started and first bidder is in, you have an obligation to stick to the agreed terms.
Hi
actually, if one starts an auction here, say in "$1 Auction" section, they must state a fixed ending time and date.
so, theoretically, the auction has begun, once the OP hits the post button and the thread is created.
now, in that section "all auctions must last a minimum of 72 hours", therefore if no bids in that period, and if the OP states that it should only last 72hrs, then the auction would end.
the OP could restart another auction for the same domain "7 days later".
It's your choice to set the amount of time for your auction, but it must last at least "72hours" if posted in that section.
one could post an "anti-sniping" rule, where it could extend an extra "5 minutes" if someone bids in the final 3 minutes.
moderators are not here to change the terms of your auctions, you should manage your own sales threads. Setting them to extend or end at a period which will deliver the results you desire.
i do agree though, that "once an auction has started, that you have an obligation to abide by the original terms of the sale/advertisement/auction,etc.."