If my 2010 Hyundai tucson is driven atleast 16 hours a day and night, mainly city driving, when should i replace the brake pads?thank you!

Change them before the brake material is depleted. Nothing beats a set of eyeballs to inspect how much brake material is left and to check for stuck calipers or brake pads. If you're concerned, have an independent shop perform an inspection for you.

If you are doing that much driving in the city. You should be getting your brakes check regularly, at least every 3-4 months. You can't prevent the pads and rotors from wearing out but you don't want to do any damage to the brake calipers themselves. Which would add a lot of cost to having your brakes replaced. Hopefully this will help give you an idea of how to do maintenance to your vehicle and not repairs. Thanks Bobby