You can do the following:
- turn off the phone by pressing "Vol Up", "Vol Down" and then hold "Power"
- turn on the phone by pressing and holding "Power"
- when the Apple logo appear - keep holding the "Power" button and at the same time connect the iPhone to the Macbook
- at some point the iPhone'll go into a recovery mode and provide "Update" and "Restore" options
- you need to choose the "Update" the phone (it won't erase the phone, just update the iOS)
- after it updates to the latest iOS and reboots - the 8hrs counter should be back (at least it worked in my case)
If the update procedure doesn't bring the timer back - the only way is to restore I believe.