I found a circuit that uses a 555 timer to turn on for 0-10 seconds and off for 0-100 seconds (It's called a programmable timer in the book, but the timing is actually adjusted by potentiometers and by using different capacitors). Circuits such as this are not hard to find schematics for and allow you to achieve the desired result without messing around with, and possibly slowing down your code. (also, they will continue to blink when the robot is disabled.
Edit: Here is a good reference to use when designing 555 based timers:
http://www.kpsec.freeuk.com/555timer.htm#astable