For a first charge, I guess something like 16hours at least is correct. For the other charges, I recommand about 7-10hours. A longer charge does not hurt the ti 84 plus C se.
If you have the dock, you can charge 10 ti 84 plus c se, it will last a night
More informations :
Recharging: two terminals on the lower sides
Power: Rechargeable lithium-polymer battery, ~5-10 hours of use
Battery Life: Officially 5 days of classroom use or 2 weeks of homework use