We hear this question asked a couple times a week.  When is the best time to calibrate?  There are two approaches.  The first is to wait until the quality of the scans deteriorates and/or if autosize is selected the scanner is not picking up the correct size.  The second approach is to schedule a calibration every few hours/days/weeks/months depending on how much the scanner is used and how dirty and dusty the originals are. 

If waiting for bad images is not an option, start with the approach first as a benchmark.  Make note when quality goes bad and schedule a calibration before the average fail event.  This can be in the morning before scanning operations start, at the end of the day as a final shutdown process or in some service bureaus between scan jobs or at break time. 

Calibrating scanners does not take much time and provides a nice break for scanning staff.  The bottom line is keeping your scanning equipment in the best condition as possible.  Remember before calibrating, clean the glass and rollers to remove dust and dirt.