After treating a wasps nest or an area where wasps are hanging out it can take 2 hours to 24 hours for all the wasps to die after the area is treated.
There are some wasp sprays though that you can buy in Hardware Stores that does Kill Wasps on contact and I've bought some before and it works.
The Wasp Spray I bought that Kills Wasps on contact is Raid® Wasp & Hornet Killer which allows you to spray up to 22 feet away keeping you safe and allows you to kill the entire nest of wasps on contact without waiting.