Up here in Northern Canada, we have a wide range of temps from +90 in the summer to -40's in the winter.
I keep my working shop (I have a 6000 sq foot building, but heat only 2/3 of it with the rest being storage) and finishing room at around 65 F during the winter months.
You have to, after catalyzing the lacquer - thin out to the required viscocity regardless of the amount of thinners you need to add. In the winter I am thinning by approx 1/3, compared to 10% in the summer. I also add a slower evaporating solvent to allow the finish time to flow out.
The other thing is to keep your material stored OFF the concrete - I keep my 5 gallon pails stored on shelving as not to be in contact with the floor which is cold.
You need to heat things up - I would say 60F is minimum to get a decent finish and an extra 5 degrees is even better.
When you turn on the exhaust (I know you are spraying in a garage so Iwill assume you dont have an engineered booth) you will be drawing in cold air so you need some way to replace that heat quickly. I have hot water rads to extra heat to the finishing room in the colder months, and it works great at a constant 64 or 65F.
If you dont know how much thinners to add, start adding more and try spraying. You can see when the spray pattern is a fine mist VS coarse droplets. You should not have to crank the air to atomize the fluid properly either as that introduces more issues..