[AC Question]

how long time charging samsung s7 edge for the first time

[sfoLAX]

Basically until it's full or longer. You can leave it plugged in. The phone cobtrols the charge and will occasionally trickle charge it between roughly 98 - 100%.
You can't do any harm.
Best though to deplete it from 100% to 30% and charge it fully a few times to calibrate the readings.
The GSam battery app is very good, especially for overheating warnings.

[Rukbat]

It's not only to calibrate things (which you can really only do by watching the battery terminal voltage change - there's an app for that - Battery Calibration (Root) [but the phone has to be rooted]), it's used to condition a battery that hasn't been used in a few months. Charge it fully (about 30 minutes past 100%), then use it until the phone tells you to recharge it (or the phone shuts off). Do that 3 times. (Don't rush it - if you don't use the phone much, it could take 3-4 days to discharge.)