One particular design issue that needs to be resolved here is that there is no need for the hustle alarm to sound when closing a local door (if the regs require it, they need changing). The member of staff knows they have pressed the close button, and they are there to verbally instruct people to stand back until the door is closed. This would easily save about 3-5 seconds from a passenger-door dispatch. Doesn't sound much, but 5 seconds multiplied by about 15 stops is a minute and a quarter (think the likes of the Southport line).
Similarly, a lot of time can be saved by following SWT/SWR's example of not requiring the guard to step out and do a platform check if he knows already that the train is platformed based for instance on where it is stopped in relation to a marker. That's easily another 5-7 seconds per station (and makes guard release pretty much equally quick as driver release).