Hi
Apple advises that you can charge Apple Watch whenever you want. The battery on Apple Watch cannot be overcharged (there is also no need to let the battery discharge to any particular level first, nor any benefit to be gained from doing so):
Batteries - Why Lithium-ion? - Apple
Apple's tips for maximising battery life and battery lifespan on Apple Watch are detailed here:
Batteries - Maximizing Performance - Apple
Charging will stop automatically when the battery is fully charged and start again if and when required due to ongoing battery usage.
Be sure to follow Apple's safety and handling instructions (see the links below) and also note that:
- It is not possible to turn your Apple Watch off whilst it is on the charger and connected to power - this is normal.
- It is also normal for your Apple Watch, power adapter and charging cable to become warm when connected to power.
You may also find (the optional) Nightstand / Bedside mode useful:
Use Nightstand mode on your Apple Watch - Apple Support
More information:
Apple Watch - Battery - Apple
Check your battery and charge your Apple Watch - Apple Support
Keep Apple Watch within acceptable operating temperatures - Apple Support
Important safety information