Knowing the way bureaucracies work, they wouldn't manage to get the order to force them to update the canary until a few days later, at which point it would be too late.
All they need to do is buy themselves one day, and have a track record of not being late with the updates.
They already have an obligation to keep the warrant secret. If the court rules that they (obviously intentionally) violated that obligation, they will bear the consequences, right? The whole point is to try to avoid legal responsibility. Otherwise they could just post the details of the warrant on their home page.
All they need to do is buy themselves one day, and have a track record of not being late with the updates.