It depends to some degree on the reg and on the tech. I like SP regs and do a lot of them so I can whip out a simple SP reg like a Mk 2 R190 complete with ultrasound cleaning and pre and post bench testing in under an hour if it is in good general condition.mike_s:next question on this.
How "long" does it take to service a regulator set? (1st, 2nd stages, gauges, etc).
I would imagine it would take an hour or two easy if you do it right and run "test" on it.
Other more complex regs take longer and regs that I do not work on as frequently take longer still as a greater level of care and more reference to the service manual is required.
O2 cleaning for use with mixes over 40% usually will add an hour on top of the annual service.
If the reg is badly encrusted, hard to get apart etc, an overhaul can be a very long half day process with perhaps a week to ten days in the middle waiting for new parts to arrive to replace the corroded ones removed. Those services are never cheap.