How many seconds to the end of the auction can I go and still be safe?

I recommend to keep it at about 5-6 seconds (that's the default).

Darn I was hoping I could do like 2-3 seconds

You can put ANY time you like. The less seconds you put, the higher chance to miss due to networks lags and other external possible issues.

There's a Polish sniper called Snip It that shows their average times for eBay - just under 2 seconds.
But by this stage (under 10 seconds) your only competition can be another snipe engine, so does it matter?

hebbzee wrote:
But by this stage (under 10 seconds) your only competition can be another snipe engine, so does it matter?

That's correct. For times lower than 5-6-7-8 seconds or, that would not matter because your other competitor is another sniper (who set their snipe long time before in advance).
So a manual bidder won't have enough time to react anyway.

* Southampton University has done some impressive research from which they deduce that 20 seconds before ending is the optimal moment for snipe bidding on eBay, bearing in mind how Ebay's software works:
The Effects of Proxy Bidding & Minimum Bid Increments within eBay Auctions http://eprints.ecs.soton.ac.uk/12716/