The interval ended up being about 10 min between shots. I took the pics every 120 seconds, but the movie was far too long, so I used the software to only process every 5th frame.
This was shot with a cheap little 1.3mp webcam, and a program called YAWCam, it is really easy actually and also runs my live stream so that I can check in on the tank when I'm on vacation.
For my next trick I want to shoot the same thing with replanting the tops instead of topping the plants but shoot it with an HD webcam, but I'll have to see if work will let me borrow one for a month,.. and that will have to be after I move.
Thanks for the interest and comments everyone!