My first encounter with decimal time was through science fiction. Star Trek used stardates, which were originally four digit numbers plus one decimal. In college, I learned that astronomers actually use numbers similar to that to date star observations, called Julian Dates, which use the decimal to represent the time of day. Decimal time standards are also found in various other science fiction works, like Battlestar Galatica, Metropolis, Asimov, etc. The Doctor does not use decimal time AFAIK, but I would not be surprised if some alien race did at some point in the lengthy history of the show.