I wish there was an exact science to your question as we all searching for the same thing. One good thing to do is to update around big title comic update that are similar to yours. This is when there is a lot of traffic of people going to check them out, some might stay and see what is new in canvas side. Is not exact science though.
In all honesty the best is just consistency on your part (update same days and around same time always). Do find a sweet spot for you though.