England has decent, sometimes outstanding weather, for about 6 months of the year - late spring to early autumn - with occasional upsets. We rarely get hot humid days. DT is an Australia-only product at the moment, so have no idea what the drying times for that are like over here, but spray paint drying times are standard. And as DT can be easily used indoors, I wouldn't see any problems with a typical indoor 22-23°C and 45%-55%RH.

Because I need to work outdoors when spraying and sanding, I'm frustrated by the cold and rain for around 6 months of the year.

Scotland and the north of England are generally a few °C colder and wetter, Wales is about the same general temperature but most places are wetter. But indoor conditions are very similar in all locations.