BTW, I have seen a lot of places where freezer heat exchangers are kept sitting inside trapped in their own heat with fans furiously running warm to hot air over the radiators. They need to duct air but they don't.
Look into spraying water mist on the radiators (cooling lines) when they are hot if you can't get cool air. The transfer of heat to vaporize water is large though you only want to do that when humidity is not extreme. That to compound the efficiency you are already wanting.
Lastly, why go by time when you should go by air temperature over the radiator?