I have found white spirit to have the least negative effect on my specimen. Acetone works well, but it can darken specimens. All of these liquids are pretty heavy and can bend wings during the drying process and hair will stick together when not using some sort of hair dryer or fan to dry the specimen. Some of these compounds can have negative effects on your health. Personally, I would not use toluene for this reason.
And to answer the original question. It depends on the specimen. Between some hours and a day or two.
Last Edit: Nov 7, 2020 10:21:11 GMT -8 by nomihoudai
I always use acetone and never have any issues. I deep all specimen and if too much oil is coming out of abdomen I do few baths in new acetone. After the acetone evaporate I immediately place specimen in relaxing box for a day and spread it so there are never curled up wings and at the same time if some scales/hairs are stick together I try gently to brush them.