I pitch the yeast re-hydrated at the time of bottling. You shouldn't be bottling if there is still sugar for the yeast to 'take off' eating, so adding early doesn't make sense. I only do this with really big beers and/or beers that have been aging for a while (original yeast has mostly dropped out and may be stressed anyway).
If you're only at 8-9% abv and haven't left it in a fermenter for a few months, I'd not bother. If you're there or higher and have aged it a while, you might as well re-hydrate half a packet of yeast while you are waiting for priming sugar to cool. I (sanitize everything, then) dump sugar in bottling bucket, start siphon with hose angled to stir beer in with priming solution, then add the re-hydrated yeast once the beer has mixed in just a little (so the priming solution's temp is brought down by the beer temp). You can also add a sprinkle of yeast nutrient to the priming solution to ensure you get good carbonation.