Getting time for beat in milliseconds with PyGuitarPo

Question

I am trying to parse tracks of .gp5 files with PyGuitarPro, but i don't understand the meaning beat.start value. My goal is to add the starting time in milliseconds from the beginning of the song for each beat, but when I try to play the track parsed with my current code the time is distorted.

Docs: https://pyguitarpro.readthedocs.io/en/stable/pyguitarpro/format.html#module-guitarpro.gp5

I can get the tempo, time signature info if needed.

def get_track_frets(self,track): #returns array of beats with time and [string, fret]
    beats = []
    for measure in track.measures:
        for voice in measure.voices:
            for beat in voice.beats:
                new_beat = {"start" : beat.start, "notes": []}
                for note in beat.notes:
                    new_beat["notes"].append([note.string, note.value])
                if len(new_beat["notes"]) > 0:
                    beats.append(new_beat)
    return beats