one very important thing people tend to forget with air dry products,, well all products actually is the rule of 15,, if its 15 degrees cooler it takes twice as long to dry, if its 15 % higher humidty it takes twice as long to dry. To make across the board statements about dry times without taking into account the number of coats of material, the temp , the solvents, and the humidity is a bad idea!!!
Ok so to anwer the question, first statemtent,, ( i have to say it) urethane over clear isnt a great idea,, but,, if your going to do it,, then, I would test my laquer for being dry enough by lightly scuffing a spot of solid color , the last color sprayed,, you shouldnt really smell any solvents after you lightly scuff it. think scratch and sniff,, In other words, take some 600 grit paper and smell a small spot, then scuff it wet, dry it and sniff again, there should not be an appreciable difference in the aroma.