It's all a matter of technique and timing. Also the products you use make a difference.
So for example, if you need to wash the vehicle and the sun is blaring, you can do a rinseless wash, pannel by pannel and you will be fine.
If you need to polish or compound the car, there is usually a part of the car in the shade, so start there and chase the shade around the car.
For LSP it's usually a non-issue.
I am mobile and for me the opposite is the problem. When weather forecast says 10% chance of rain with no accumulation, and it starts to rain, it usually throws my whole day up because I did not plan for it and there is very little exterior detailing that can be done in the rain. For interiors you can always find a way if a little rain comes but for exterior, you are kinda screwed until the rain stops.