Change boundary conditions during a heating process

Hello,

In an heating simulation, I would like to change a boundary condition during the simulation. I would to impose on this boundary:

1. a heating condition during 600 min
2. an tempering condition (no heating, but there is conduction in the material) every 20 min for 5 min.
So,
0-20 min: heating
20-25 min: tempering
25-40 min: heating
40-45 min: tempering
...

Is it possible? With the solver sequence? How to do it?
Thank you. Howard