Put your camera into custom timer drive mode (exists at least on my a570is) with your desired delay (0 to 30 s or similar in my camera) and number of shots (10 max on my camera) and use CHDK built-in continous mode bracketing (+, - or +/- as you wish) from the extra photo operations menu.
These features are not present on 720is, I can bracket within CHDK but I need to keep my finger on the button.
+/- 10 shots?! What for?
BTW, the camera allows you to shoot in burst mode 1-10 shots, with a delay between 0 and 30 seconds before the sequence. No scripts needed. You can go as far as +10EV/-10EV. It's also fast.
10 shots was just a number that would be useful to me, 5 might be OK but up to 10 would be ideal for me and maybe of use to someone else who would play around with HDR.
CHDK takes care of the bracketing, BUT YOU STILL HAVE TO MANUALLY HOLD DOWN THE SHUTTER otherwise you only get 1 shot.
Experienced this and re-read page 87 in Canon manual.
Regards to both,
Papaone