Ideally you want to have an idea (by idea I mean a list) of the program that you want to apply to the summer before the application cycle. People are saying the earlier the better. However I will say there's a caveat to that! You can only get so much information from the website, plus occasionally the recruitment  website is outdated. Sometimes it is super helpful to just talk to people: in my case, I have a handful of programs that I want to apply to though I still asked my professor for recommendations i.e. if he has some good mentors/programs out there. The benefit of asking people is that they might have connections to some programs/faculties which you won't have any idea until you asked. It is also true that if you apply to someone who is in the network, you have a much higher chance of getting into the program compared to if you just apply randomly and roll the dice. 

 

Also it doesn't hurt to reach out to the potential faculty member before you apply. In fact, I highly recommend doing that. For example, if they indicate that they are not accepting students on the program website, you can still email and ask. I mean you're not gonna lose anything by asking.  The reason why I said this is this literally happened to me before: I emailed and a faculty member replied saying he is accepting students even though on the website it said no. 

 

It is a good idea to reach out to your prospective program coordinator as well. A graduate school application costs money, and it's a lot considering you are not just applying to one school. Here's the deal: you can ask the program coordinator for more information about the program, i.e. maybe set up a time to chat AND in the meantime ask if there's an application waiver.