Dave: Everyone knows that time passes far quicker on the customer side of the bar than on the side of bar staff.

Not quite. In these circumstances time is relatively relative.

For most of the evening time (for the customer) flies by, while time for the bar staff can tend to drag.
Except . . .
When you order a pint. For the customer time waiting seems to drag, while the bar staff seem to perceive time moving more quickly.

Cheers!