The remaining time is always displayed at the bottom left corner of the main home screen after the letters "REM". It is displayed depending on how many tracks are currently armed for recording. If one track is armed (Flashing RED) it may read 125h00m, which means 125 Hours of recording time on that ONE Track. If you arm two tracks (Flashing RED) for recording that time will CUT exactly in half with a remaining time of 75 hours of recording time.
To calculate how much continuous recording time is available, you simply divide how many tracks into the totaly amount of remaining time with only one track, or simply arm the tracks and it calculates it instantly.