Li-Poly batteries, so the memory problems of older batteries are minimal to non existent.
Li-Poly batteries are also shipped and stored with a decent percentage of charge in them...they last longer on the shelves that way.
Plug it in and give it 10 or 15 minutes to trickle in enough fire to drive an atty.
Avoid the dual or triple coil stuff unless you're going to charge it fully before hitting it, as these things call for mondo amperage. You might also want to reach for your regular or hv (single coil 2.5 Ohms and up) stuff if you have a choice in the matter, as the LR stuff will ask for more amps up front.
With any other atty/carto....
You can surely toke it moderately while it's still plugged in and charging.
Within' an hour or so you should be good to hit it as hard as you like even if it's not fully charged yet
You certainly wont be the first to toke away with fairly low battery on a brand new Darwin on a usb cord
What's great about the Darwin, is you get the same power every toke....from fully charged to the last toke it can deliver. Several folks have suggested not to let the Darwin battery drain fully if you can avoid it....but I think it has internal electronics to prevent you from damaging the battery...plus it is warranted for a year. So enjoy