When to apply for master scholarships?

I'm guessing that the intent of this is to determine if you are in the somewhat rare case of not needing funding. If you can say that you will be funded from other sources (scholarships from another country, for example) then funding is one factor the committee need not consider. But if you need funding, then they also need to find ways to provide it if you are accepted. Or at least think about that, since if you are accepted without any funding, then there is a higher chance that you won't actually come.

So, follow the rules of any scholarship application, of course, and answer this question honestly. Apply when you meet the criteria.

I doubt that they expect you to have funding already arranged. But they would consider it a plus if you do.

Depending on your program, most if not all recommend applying for external scholarships prior to acceptance into the program (as if you are already going to attend). For the big government scholarships, the application date for study beginning next Fall has already past, but provincial awards (such as OGS in Ontario) are open until early December. Internal awards are decided during the application process usually. It doesn't look great if you apply to a program without attempting to get any external funding, but it's not absolutely necessary.