Methods, apparatus and systems are disclosed. In one embodiment, a method, implemented by a Wireless Transmit/Receive Unit (WTRU) registered to a first network, includes receiving, from the first network, information indicating a value to be used during a registration to a second network; and determining, based on at least the indicated value, at least a first start time and a second start time from which to perform the registration to the second network. The method further includes initiating the registration to the second network after the first start time; and on condition that the registration is not completed within a defined period after the first start time: (1) halting the registration to the second network, and (2) initiating a second registration or re-registration of the WTRU to the second network after the second start time.