There is no real established guidelines on this.
A flight can be cancelled at any time for any reason. Airlines will keep telling you that they will notify you as soon as "reasonably possible". That is, the time between the reason for the cancellation and you being informed should be kept as short as possible (e.g. there is obviously lag time where the airline decides what to do about the situation and then creates an approved communication to you about it, but simply putting it in the "too hard basket" and letting it sit for a while without address would be an example of unreasonable delay in informing you.)
The policies around cancellations more apply to what happens after the cancellation (e.g. compensation) compared to how and when an airline informs you (the latter is fairly stock standard, unless the airline completely screws up). Unfortunately, with the exception of the EU, there are not many gazetted cancellation policies around redress and compensation for cancellations! Most will offer you a reroute or retime within reason, but this is not documented and often if you don't accept option #1 you will need to put up a small (or large!) fight to go for other options. Refunds or even credit for later travel gets more complicated. Some of these you can argue for based on other statutory codes (e.g. Trade Practices Act).