I have used CHDK for several years, mainly for Aerial Photography. A interval script is a quick way of taking AP photos, but a RC remote control is better.
Here is a freeware (for personal use) RC remote control for CHDK that I have designed, all you need is a 12F683 PIC processor, some cables and access to a PIC programmer (circa $20 to buy).
Source code in Mikrobasic proivided, which is free to use for the 12F683. Documnetation and build instructions provided.
If you want to play with the source or diagnose issues, it sends debug output (such as measured RC pulse width) to a RS232 terminal, audio as Morse too.
http://www.rcgroups.com/forums/showthread.php?t=1387378 Stuart