This!Yes there are sleep monitoring apps, though not a native apple one.
I charge my watch in the morning while I eat breakfast and shower. It doesn't take long to charge, about an hour to go from 0-80 and another hour to top off to 100. My watch is usually about half way charged in the morning, so charging it for 30-45 minutes while I get ready is plenty.
I have a series 3
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What version do you have?
I also charge it during my commute.