I would like to execute a function for X seconds every Y seconds on Arduino.

I'm trying to control a resistance to heat up some water in a constant rate (1o Celsius per minute), so what I thought was: I'll measure what is the rate when it's running for the whole minute and then I'll adjust it to the desired rate.

Let's say it heats up 5o celsius per minute, so I would like to activate the resistance for 60/5 seconds, but not all at once, I was thinking about activating the resistance for 1 second every 12 seconds to keep the rate constant for no matter what (if the day is too cold, too hot, if I change my equipment etc.)

Do you guys think this is possible? If not, any ideas how can I make it work? I saw the Timer.h library but it doesn't seems to solve my problem =/

Thanks in advance, please let me know if any information can be useful!