It depends - we're pretty quick at processing exchanges, and begin to do so as soon as we get the paperwork in front of us. This is usually around a week from the day you popped your return in the post to us, but sometimes quicker.
You'll get an email from us as soon as we begin processing your exchange, and we'll send you another email to let you know when the new size is on it's way.
If we don't have the new size you requested in stock (or if you have requested an exchange to a different product), we'll send you an email to let you know that we've refunded you.
If you do need to get your new item quickly, it may be worth asking for a refund and then placing a new order online.