The most appropriate time to approach a nest is at night when all wasps are present and sluggish. It's possible for you to use WD-40 to spray the whole nest but you must get all of the nest because if you miss they'll attack. So I recommend good quality wasp killer after you learn - how to get rid of wasps.
At night when there is no sign of any wasp activity apply your wasp killer directly through the opening of the nest. Make sure you have pre-read the instructions! You don't want to be reading the instructions while performing the application as the wasps might attack.
Never stand just under the nest as the insecticide will just end up falling on you and you might not correctly soak the nest. Ensure you have good access to the opening of the nest so that you can get as much insecticide inside as you are able to.