Enquiry emails for grad school I will be applying for grad school soon and have drafted a few informal enquiry emails. When would be the best time to send out informal enquiry emails to potential supervisors? Would it be advisable to send them out as soon as the programme starts to accept applications or even earlier than that? I'm asking  particularly for US universities.
Thank you!
EDIT: Since a lot of people have said this is field related, I thought I'd mention which field I'm applying for - I'm applying for microbiology/immunology programmes
Most professors that I know in the US (in computer science) do not want to receive such emails and will ignore them. Many have a note on their website saying so. The expectation is that students should submit an application and only after they are admitted should they talk to faculty. If you are interested in a particular faculty member, you should note this in your application.
That said, norms vary greatly. In the UK, the expectation is the opposite in my experience -- you should only apply after contacting a potential supervisor.
You should look at the websites of faculty that you are interested in working with and see what they say about contacting them. If they do invite such inquiries, then you should contact them. In terms of timing, earlier is generally better, as long as you are at the stage of having reasonably concrete plans.