Until your substance is solved in methanol it cannot get hotter than 65°C (boiling point). The main problem is overheating after evaporation. It is much better to use a hair drier first at medium, later at low temperature.
In general I think UV / oxygen destruction of this class of compounds is a bit overestimatet. It is definately a problem if you store microgram quantities for longer periods on air. But fast evaporation without overheating or handling under room light should not be a real problem for milligram quantities.