Right, but we think the federal standard should meet or exceed the best provincial standard, and the best provincial standard is Saskatchewan, which requires one week's written notice of your schedule and of any changes to your schedule.
Twenty-four hours just isn't enough, for a number of reasons. For example, if you book a medical appointment, a lot of establishments will require you to give 48 hours' notice for cancellation or you have to pay a fee, so if your employer calls 24 hours before and says they need you to come in and you're not allowed to say no, then you've incurred the fee and you don't get to have your medical appointment.