To see a doctor in a clinic, you don't really. You call, schedule an appointment, they get you in same day.

To see your GP is a bit trickier, but generally they can get you in pretty fast when needed in my experience.

Certain other 'functions' like getting an MRI take longer. Few months on that one. I'm still waiting on mine, and it's because I'm 'low priority' now that I've been diagnosed already.