Updating a clone with Time Machine

Fortunately my Mac is running OK. However, I do keep a clone (which I redo from time to time) of my hard drive on a second internal drive, and back up using Time Machine. I use the computer in my work and can't afford any down time. If my main hard drive should fail, I could boot directly into the clone, but would need to update the clone with the latest backup in Time Machine. How would I do that?

Thanks.