Before transferring a domain, you should check what the expiry date is. To transfer with all guarantees, our recommendation is to start the transfer at least 15 days before the expiry date.
The domain transfer process can be very fast — even less than 1 hour — but it can also be very slow if the people who need to authorize the transfer take their time doing so. That's why it's best to do it with enough time so the domain doesn't go down because the renewal date arrives before the transfer is complete.