It depends on what you mean by "heavy." If you have in mind a rush of bids that would resemble a Sunday evening, then yes, by all means allow more lead time on your snipe. eBay's servers can handle most traffic and it's only the very busiest times that jam things up. AS's servers rarely if ever are overwhelmed so that's not a worry.
You can perform a simple test about 10 minutes before your auction closes by using eBay's search program to look for something, and then clicking on one item in the resulting list, noting all the while just how long it takes eBay to respond. That's just an indicator, but at least you'll have some idea of traffic on eBay at the the approximate closing time.
Just remember that you cannot change or delete an AS snipe with 3 minutes or less left in the auction. AS is locked in at that point and accepts no revisions. By the way, as a general rule of sniping you should not bid at all until your snipe comes due. You want to swoop in out of the blue.