Every year i post - I have a cutoff of March 26th - no new returns after that point. I'll accept remaining only data through April 8th. Of course there tend to be exceptions but for the most part my clients work with this.

By March 26th I have a backlog from uploads, dropoffs, waiting for info, etc. that stretches miles long. I need those three weeks to get to everyone. 

Otherwise every client would try to schedule an appointment April 10-15th.