The fuel filter is the first place that the fuel gells up (assuming an engine is running). The gell point for #2 diesel is just under 20 degrees - at which point wax crystals will start to form in untreated #2 and clog the filter. Once the fuel re-warms, the wax dissolves back into solution, unclogging the filter and allowing fuel to reach the injector pump.
Gelled fuel does not stay gelled once the outside temps warm up. It's not like making Jello. Once the fuel is warmed and the wax crystals are dissolved, it is exactly like any other diesel fuel that has never gelled. It's like comparing water to ice. Once ice is melted, it's water.