Timing
The correct time to remove the shoes is around about the time that your horse would normally be due for shoeing. There should be sufficient hoof growth to perform a simple setup trim and for your horse to be comfortable.
Meeting your horse when shoeing is due will also give your trimmer a picture of how much hoof he normally grows, how he grows his hoof, and the wear patterns on the shoes.
If, for any reason, you have left the feet too long between trims and the feet have grown very long, then it is important that you get them trimmed as soon as possible. Long feet can increase the mechanical loading on the laminae and lead to stretched white line and also are more prone to breakages of the wall.