IF all you are suffering from is a satellite lock problem (and not the time being goofy) then here's what I would recommend.
Delete the CONTENT (not the folder) of the folder on your device called "ephemeris".
Then on your PC, find your TomTom\HOME\Download\complete\ephemeris folder and delete the CONTENT (not the folder) of that "ephemeris" folder as well. That will mean deleting one or more folders called "QuickGPSfix".
Then hook back up to Home and get whatever QuickGPSFix file it offers and see if that doesn't get you a decent satellite fix after a couple of minutes.
Following some test use in which my 910 would take around 2 - 5 mins to become live enough for navigation and sometimes not at all I updated the QuickGPSfix file. The unit now operates with no problems.
I did not delete the ephemeris files.
Many thanks for your assistance.
Ah .. we had assumed that you periodically updated your device. Might be good practice for the future. What can happen is that a bad internal date mechanism on a file can cause an old file to be used far beyond its useful date. If that winds up in your ephemeris folder, it can prevent future updates to newer fix files.