That is strange. How about a washer or two between the mounting tab and the plate so the clock won't get pulled forward when tightened....if that's what's happening?

 

Camaro69

Your right yesterday Sunday morn I removed the lens from the clock then mounted it into the plate.
I noticed it was a little tight and pressure was up against the clock. So I bent the top tab up just a little then screwed it down.
It has kept perfect time.

So this morning I am going to put the Lens back in and try it that way and run it for another day. Will let you know the results, and thanks for the advice.