I tend to calibrate my projector every time I move my printer/projector, or give it a hard bump. You would also want to calibrate anytime you feel like your dimensions are incorrect!
If you keep your printer in a very stable place, then I wouldn't expect you to have to calibrate very often.
Note that I don't use a LittleRP (Yet...) but this has been my experience with other printers.
Calibration for XYZ dimensional & scale accuracy: How often?
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