Last time I shot every 15s to 20s. Exposures ranged from 1/250s up to 5s during totality. I only changed ISO close to totality and I think it might have been ISO800. Otherwise it was 400 or 200 during the bright phase. I found shooting every 20s gives you plenty of time to refocus or recenter if you need to without interrupting the imaging. I got a bit over 1000 frames which gives you a nice length of video played at 25fps and also not too much to align and process.