Hi there, I’m a ruby on rails developer as well and glad you started a project in rails. However, you might want to be careful with memory allocation on the Pi. Rails isn’t really friendly on RAM. Pi rev1 only has 256mb Ram.
As for the the interval scheduling, I used on my project a start date, with an interval. Ie: Monday 9th June 2013 6:00AM. Every week. I use a runloop to check sqlite if I have a matching interval and then open the relays with the matched scheduled. I don’t know if it makes sense.
Good luck !