On April Fools Day one year a Sydney radio station announced that, since Australia was now using metric weights and measures, they would in future be using only metric time. He then announced, "It is now seven point one five" which was, of course, 7:15. There were howls of anguish across the city and the radio station's switchboard lit up with calls from anguished listeners.
When you say digital time I wonder if you mean 24-hour time? That would be 0215 for 2.15 am or 1415 for 2.15 pm. Or, if you just want to write it digitally then, as everybody pointed out, it's 2.15.