Originally discovered in iOS 11.4 beta code by ElcomSoft's Oleg Afonin, the update disables the lightning port after the seven-day period, though it can still apparently be charged. The feature is called USB Restricted Mode, and it made a previous appearance in an iOS 11.3 beta. Afonin noted that law enforcement will now only have seven days to attempt to access any iPhones running 11.3 or later before it locks itself against any "known forensic techniques."
Prior to this new addition, anyone could create a new local backup of an iPhone or iPad using the lockdown record extracted from the computer associated with that iOS device, though those records did expire after a certain amount of time, according to Afonin. Now, law enforcement will have an expedited window to unlock the device, as the lockdown records also expire after a period of time.