darylgo, I can't remember! I just read the manual (if you don't have one I think you can download it from Hasselblad, free, you just need to register) and stumbled on to it. I'm not at base for a few days, so from memory, you set up the user button, the one beneath the middle bit that you push to format the card, (hope these technical terms don't baffle you...) so that the mirror goes up (maybe by assigning that function to that button, in the custom settings - but you can still use the main mirror-up button as normal), also in custom settings maybe you set the interval timer to 5 secs, or whatever you decide on. Can't remember how you get the mirror to return, but mine does. Sorry it's so vague. Maybe if someone reads this and has the manual with them, or a better memory, they can explain better.
But it's a great way to make exposures and you don't need a cable. When I first got the camera I was losing loads of shots, maybe 50%, to poor technique thanks to years away from MF and relying too much on auto DSLRs. Now I take most stuff on a tripod, often set it at f16 if I' m after big DoF - slight diffraction but worth it for extra DoF and easily compensated with a bit of sharpening. Without BS, I can't remember the last time I had signs of blur from mirror slap/camera shake. The great thing with the all-leaf shutter Hass lenses is just that - leaf shutters.
