1 year after the day it was done.That's my question too. Also, when is the expiration date for a medical exam? The day it was actually done or the day it was approved by IRCC?
One's COPR is valid if medical results are valid; therefore, one's medical should be valid at the time of landing. If one's medical is expired before receiving COPR and after the passport sent for counterfoil, the passport will be returned without the counterfoil therein, and the COPR will not be issued. Hence, if the medical expiration date is close, it is common practice for the IRCC to let the medical expire and then either request an extension or instruct for a remedial.