90 day prescriptions generally require the Dr to write a 90 day script. You don't need to do mail order to get a 90 day fill. It is the insurance companies that set the amount of time that a script may be filled early. We have used GoodRx and Kroger Savings Club to fill ahead of schedule, and just did for 4 months away. It cost a little more in co-pays--a convenience cost for us. Any drug store will transfer from another regardless of whether they are in the same company or not. But you will then have to transfer back. The chains like CVS or Walmart probably make that easier.