File format question?

Synthesizer V stores the vocal track in text based (Json?) file format. This is very nice! However, I can not understand how the time is represented - both the start time and duration of the notes are very big numbers.

Do anyone know, how the time is represented (for example, what is the value of quarter note in 120Bpm)? I am asking, because I would like to generate and process new vocal tracks with my own algorithms.