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.
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