I suggest setting your Auctiva to whatever Time Zone you find it easiest to THINK by. It will then post according to the appropriate time in the time zone you Think in. eBay, of course, will show the Pacific Time equivalent.
I would say you're worrying too much (a common rookie mistake) about a small time variance. Even if you're a little 'off peak' in one time zone, it is 'prime time' in another time zone. Also, most buyers find your listing by searching for a particular item - not by browsing a given time slot. It's far more important to concentrate on doing a good listing with a good title.
My experience, over 10 years, is that the time slot alone makes little if any difference in results. A good listing will sell, even at 4am - while a bad listing will rarely sell at any time.