First divide the UTC by 86400. For example, if your 1448463066.539 was found in Cell A2 you would use this formula: =A2/86400 this would return 16764.6188256829. Then you would format you cell in the following user format MM/DD/YYYY HH:MM:SS.000 . This will return 11/23/1945 14:51:06.539
If you notice a slight time warp in this answer, I did too. How to fix this was the question I was going to ask when I found yours. I think the time is set wrong on the meter.