I've experienced this same problem for the last week. I started with 5 seconds and now I'm up to 10 seconds and I'm still getting "Not In Time" messages/results.
I've never had to go any farther than 7 seconds during prime hours in the past and in most cases I was able to get by with 5 seconds.
I've also noted that there used to be a much smaller time difference between the AS servers count down and the times listed on the items page. It used to be 5 seconds difference, now it's like 35 seconds,....I'm thinking somebody at Ebay has figured out a way to trick the incoming snipes with a false time stamp so the only winning bids can come from proxy bids from Ebay.
I may be wrong. But so far I'm getting told by AS that their severs and Ebay's match up perfectly as far as time stamping which I wouldn't know how they'd be able to ascertain that. They can't seem to get a winning bid in ANY auction I've sniped in the last week. 100% "Not In Time" doesn't cut it.