We normally say don't use a device that is out of date ...
I once did some work where the biomeds had no PM schedule worthy of the name (in fact, thinking back, many were like that) ... but simply relied upon user departments to check the dated stickers and alert the techs when maintenance was due. There may be arguments to support that idea (
eg:- making the users take responsibility for their equipment).
Trouble was that when a keen Head Nurse finally got around to checking her department's kit ... we would be suddenly overwhelmed with a load of (over-due) PMs. One time they even brought a whole department's worth of infusion pumps into the workshop for "immediate action".
The moral of the story? Unless the PM schedule is crafted with care, there may be days on the schedule that indicate hours of PM work way beyond the daily man-hours available in the biomed shop. Also, what if the actual due date falls on a weekend, holiday or whatever? PM cannot always be completed per schedule ("on the day"); so, there
has to be some degree of flexibility.
As I keep banging on about, properly conducted Risk-Based PM takes care of all this. In short, the work should be carried out in consideration of
priority. For instance, it may not really matter if some low-risk items never gets PM'd at all (but simply left at a "repair when failed" status). "Leeway" beyond the due PM date for more important items could (should) depend upon the priority assigned to each.
But even with a well balanced schedule (that is, with planned workload evenly spread across the calendar) there is bound to be slippage from time to time. This could be due to problems such as loss of available man-power or some other "unforeseen circumstance" that screws up the schedule.
Anyway ... who makes the rules?