As I understand it, the custom plans work the same way as Refresh in the
sense you can still upgrade at any time, by paying off your device plan
in the same way. Then you're just tied into the network plan for
whatever contract period you choose.
Going from previous years - tracking can show 1-2 days before release
date within my o2.o2 likely receive the stock themselves on the Thursday
and then dispatch that evening for delivery on the Friday. As long as
you're one of the lucky ones that is....