It depends on the type of Freepost service take up by the company receiving the mail. Average is 2-3 days though.
Hello!
I can tell from my experience that I have sent large batches worldwide, and it is definitely difficult. There are a few important things to know. First, most people don't know how to re-stretch the canvas. Secondly, how to properly pack it all in a box. And third, make sure you use professional services for this! In my early years as an artist, I used the services of this company, which delivered paintings all over the world http://fineartshippers.com/