'Way too short, bbcrafter. Five seconds lead time practically guarantees that your bid won't be registered in time by eBay. For Sunday bids, particularly in the afternoon and evening, I allow at least 15 seconds. I've been known to "stick my toe in the water" by doing a search or some activity on eBay just as a rough gauge of how busy the circuits are out there, but as a rule of thumb, allow at least 15 seconds.
If you're apprehensive that other bidders might see your bid and react with a counterbid, don't fret...the same eBay delays in registering bids applies to them, too. I'd bet dollars to donuts that no proxy bidder could get a new bid registered by eBay in under 15 seconds on a Sunday afternoon or evening.
Good luck! Let us know how it went.
