Welcome to Fishlore.
You don't really need to let the water sit overnight, you can put the tap water conditioner in the container that the water goes in and pour water in it, then add it to the tank.
Your tank is currently cycling so I'd recommend an API master freshwater testing kit and switching to Prime for your tap water conditioner, plus 25-40% water changes every 1-2 days. Test the water before each change for ammonia, nitrites and nitrates to track your progress in getting the tank cycled.