Not unless you have an old watch. I ran my S0 in Theater Mode all the time to make it thru the day. My S4 would have no problem doing what you want to do. I don't know if low power mode will restrict any sleep functions.
I charge my aluminum S4 in the morning while I have a cup of coffee and spend an hour catching up on things and taking a shower. It’s at 100% after an hour, and I wear it all day and all night after that. When I go to sleep I turn on Do not disturb and Theatre mode, just so it doesn’t bother me with lights and haptics, and when I wake up it’s usually at 60+%.
I charge my watch a night while getting ready for bed. I run it in theater mode and do not disturb turned on and its 90-93% in the morning. Still enough to make it through the longest of days.