From Justice Blair of the Ontario Court of Appeal:
It is well-accepted in the case law and in the forensic science literature (a) that the elimination of alcohol from the body generally continues at a relatively constant rate which ranges from approximately 10 to approximately 20 milligrams of alcohol per 100 millilitres of blood per hour, and (b) that, after rising rapidly within approximately 30 minutes of the last drink, a person’s BAC will remain at a relatively constant plateau for approximately two hours, before declining at the foregoing rate. See Phillips and the academic legal and scientific literature relied on therein.
CanLII - 2010 ONCA 615 (CanLII)