This would be a very round-about way of getting it but yes you could use a dwell meter. Dwell is measured 0-90 degrees so you'll need to multiply it by 1.1 as IDC is amount of time on for the total amount of time on and off (0-100%). This may or may not read the same for marine or small engine meters, but if it's for a 4-stroke it will read this way.