It also depends on what your electric costs the rest of the day. If you only mine for those 9 free hours it'll take a lot of your time (having to start/stop the miner each day, unless you script it) plus youre only mining 38% of a day. You should figure out what it would cost to run a miner 24 hours, including the 9 free hours. It might still be profitable. Or look at buying older hardware for cheap/free and run that only during the free hours.

The problem might become that if you start a big farm of old (free) hardware the power company will realize it and start charging you for the "excessive" use.