The record is 1.8s. This was after changes were introduced to try to slow down pit stops. I believe in the past signals were sent that the wheels were on before

The record is 1.8s. This was after changes were introduced to try to slow down pit stops. I believe in the past signals were sent that the wheels were on before they were fully secured (anticipating that by the time the signal was given to the driver the wheel would be fully secured). A delay was introduced and over a couple of seasons the crews managed to get back to (and beat) their old times.