It probably doesn't help you, but I have two A4000 cameras with the 101b firmware. One has the 2698 revision of CHDK, and the other the 2847 revision (both from about 6 months ago), and the intervalometer works on both. I tried the default 15 seconds, and 12, 11, 10 and 8 second intervals, and they all worked. I'll try the current version of CHDK on one of them a little later to see if it works, too.
... I tried with CHDK_DE_a4000-101b-1.2.0-3192-full_ALPHA_rev_3192, and the interval.bas script works, too, with an interval of 10 seconds.