Dead...Another good post, tack coats in cooler and less than optimum conditions, with only a medium reducer, I would would almost be a "must requirement" no matter what he paid for the paint.
What type of paint & Brand is it that your putting on the vehicle, Base Clear, Acrylic Urethane, Acrylic Enamel, Poly Urethane ETC?
Urethane's may, depending on brand, quality, reducer, hardner and especially temperature, require longer flash times and stay tacky longer than other paints.
If you can give us this information we may be able to give you better advice. Remember this, paint is paint, they all work to a degree, but they all have different qualities and act different in different situations. The more information the better the advice.
Post back soon, I'll be checking to try and lend a hand before Sunday.