Also considering this:
1) if you have a single filter and it goes out after hours, the tank is without a doubt going to be hit with lack of oxygen for the filter and tank,and the filter medium's bacteria will probably die. New filter syndrome on an already established tank(with full load) - might as well write if off as complete loss.
2) 2 filters give you the balance of water movement across a longer tank, in above scenario you still have one filter going to keep things running until the next day when stores are open, and best of all when cleaning the filter medium in one filter, the other is still active.
I would shoot for two or keep an extra around for backup