I had the same issue here on an iPhone6. Had a broken screen from which the touch functionality only worked on half the screen. Due to this, couldn't enter the passcode properly and had several wrong tries. If that happens it tells you to retry after 5 minutes. The next time, you have to wait 15 minutes, then 60 minutes etc. So I ordered a new screen and replaced it. In the process I disconnected the battery and reconnected during reassambly. This causes the date to revert to 1st of Jan 1970. Which, yesterday, was 25359778 minutes ago. I didn't want to restore the phone as we didn't have a recent backup. Also I didn't feel like waiting 48 years to retry. Finally I just connected to the mac and opened iTunes (not sure if that's necessary). I waited a bit and apparently the phone synced time with the computer. Now I could enter the passcode.