The practice of “less a day” itself is not unusual. In fact, the Controlled Drugs and Substances Act has an offence of five years less a day. It's an indictable offence; it's five years less a day.
What is unusual—in fact, it would be precedent-setting—is a ten-year less a day term. The motion would, for all intents and purposes, eliminate that precedent-setting type of penalty.