UrLog Timestamp format 171374.685

Hello, i just read a URlog with the URlogviewer and now i got a .csv with the different Values in it. I want to use it for further analysis with Python. The timestamp column i got has a strange format, for example like this 171374.685 . At first it looks like a unix timestamp, but it doesn´t make sense at all since unix timestamps dont have commas. Can somebody help me how to translate this number to a timestamp like yyyy-MM-dd HH-mm-SS?