The researchers were able to reset the one-hour counter for as long as you plug a USB accessory into the iPhone's Lightning port.
Apple iPhone USB Restricted Mode can be bypassed
With the rollout of the iOS 11.4.1, Apple made it harder for law enforcement to bypass the USB Restricted Mode. However, researchers have found a loophole.
Researchers at cybersecurity firm ElcomSoft explained:
"We performed several tests, and can now confirm that USB Restricted Mode is maintained through reboots, and persists software restores via Recovery mode. In other words, we have found no obvious way to break USB Restricted Mode once it is already engaged."
"What we discovered is that iOS will reset the USB Restrictive Mode countdown timer even if one connects the iPhone to an untrusted USB accessory, one that has never been paired to the iPhone before (well, in fact, the accessories do not require pairing at all). In other words, once the police officer seizes an iPhone, he or she would need to immediately connect that iPhone to a compatible USB accessory to prevent USB Restricted Mode lock after one hour. Importantly, this only helps if the iPhone has still not entered USB Restricted Mode."
It is to be noted that one can't break the USB Restricted Mode once it is already engaged. However, the iOS will reset the countdown timer if one immediately connects the iPhone to a compatible USB accessory.