According to Nintendo Support Center https://en-americas-support.nintendo.com/app/answers/detail/a_id/22748/kw/charge%20hours, it takes approximately six hours in order for the Nintendo Switch Pro Controller to fully charge. Once the Pro Controller is fully charged, the recharge LED beside the USB connector will shut off. This applies to Nintendo Switch Family (Nintendo Switch & Nintendo Switch Lite).
Here is a short step-by-step guide on how to charge your Nintendo Switch Pro Controller:
1. Connect the Nintendo Switch AC adapter to the dock and then to a wall outlet.
2. Connect the USB charging cable included with the Pro Controller to the controller and then to an available USB port on the dock. (Or you can connect the Nintendo Switch AC adapter directly to the Pro Controller and then to a wall outlet.