It depends on how you want to sell your item. If you set a buyout that you're confident will sell the item (such at the lowest price on the AH, or a reasonable price on an item that's not currently in the AH), then it doesn't matter too much when you put the item up. I recommend you to put to put two days, since that gives more people a chance to see your item. You get the listing fee back when you sell your item anyhow, so it doesn't matter too much.

If you want your item to be bid-only (or if you set a very high buy out price), then you do need to consider the time. I'd say to use two days again just so that people get a chance to see it, but if you can, maybe set the end time to be 10PM ish on the east coast/7PM ish on west coast US so both groups can reasonably see the end of the auction. People do tend to start seriously bidding on 'short' or 'very short', so it's in your best interest for those times to be accessible to as many people as possible. There are many players outside of US/Canada, but the ratio still skews in that favour.

As for which items to buy...Wolver, Polaris, Sealed Sword, Barb Thorn Blade/Shield, Brandish, and Owlite lines are what sells quite well from what I've seen. It really depends on the demand though, and Demonic's suggestion to make another account to check AH works (though I'm usually too lazy to use this method).