This particular response looks like it might have been created by splicing together two standard ‘lines to take’: one dealing with the recommended time to arrive before departure and the other intended to respond to comments about ‘doors locked before departure time’.
I think that’s exactly what has happened
I press 'doors close' at T-12 seconds, get interlock, check the monitors, check the signal, and wheels move on the dot.
Up to 1 minute with all the bat waving and ding ding station staff and guard stuff isn't unrealistic, but anything longer is just a bum-covering, inefficient, lazy, customer-unfriendly way to meet targets and shouldn't be allowed.
I used to find 30 seconds was about right to start the DOO dispatch procedure (check signal, hit door close, check interlock, check each monitor, check signal, final check of the monitors, take power) to get the wheels rolling about bang on departure time.
Leaving late (unless unavoidable) is more customer unfriendly to those who have boarded the train in good time.