It is 19h if you use it at the limit of its specification; 4h with the screen on. Sleep tracking uses very little power, probably uses a co-processor like the M8 that can do all that with very little power usage.
You will also notice that they have TWO WATCH SIZES. One will undoubtedly be much more than 19h, probably more like 30h of mixed usage.
As for charging, lets see; the current phones Iphone 6 battery of 1800 Mah takes 145 minutes from 0 to 100%. The smallest watch probably has a about 200-250 mah battery, charging at same speed as the Ipĥone 6 you'd get... about 16-21 minute for a full 0-100% charge... If they used something with similar amp as Ipad charger, they could do it in about 10 minutes. Though, heat constraints may limit this option. We'll see.
The Apple watch doesn't work in the shower, so unless shower+grooming is super-fast, you wouldn't have to do anything special to use the watch during sleep. Put watch to charge, take shower, brush teeth, etc... Put the watch back on and go to sleep.
There you go. Pretty sure you could have determined this yourself.