[plumbingods]

This guy did not do you any favors, trust me.

If it takes more than 2 seconds for a burner to light the after ignition transformer is energized, there is something wrong with your burner. What you have now is called delayed ignition, and is probably an air adjustment problem. If he gave it a little too much air, that can cause this condition, as well, can a weak transformer, dirty electrodes, or mis-aligned electrode tips, along with others.
There also should be no bang during start-up when a burner is running properly.

This guy is either a rookie, lazy, or just plain does not know what he is doing.

Yes, changing any one of the nozzle parameters (Gallons per hour, Spray angle, Spray pattern) can cause a different flame pattern and will need different adjustments.