By using the term "touch-up paint" I assume you have an "all-in-one" 2oz bottle of paint.......meaning, the paint is all mixed and ready to go....all you need to do is shake the bottle and apply the paint with a brush/medium.
[This is opposed to (correct me if I'm wrong) a single, double, or triple stage paint that requires the additional mix of hardener and reducer before applying the paint.]
Either way, you'll be fine. Best if not applied in the rain....but your global temp should be fine. Don't be compelled to pull the truck into the living room or run a propane heater or heat gun while applying touch-up paint. Your results will be best depending on the medium that you use to apply the paint. For example, a professional pin-stripe brush is, generally speaking, a preferred method of applying touch-up......using this method, you'll have a difference in surface--the touched up area will be raised above the base paint surface. If you have the tools and patience, you can gently sand the touch-up area to match the base paint surface level.
If there is rust in the areas to be touched-up, then you need to remove the rust first.
The most professional way to "touch-up" a body panel is to repaint and then apply a new clear coat to the entire panel.
The 2nd, more professional and economical, way to "touch-up" a body panel is to remove the clear coat in the area surrounding the flaw. Lightly color sand the paint coat of the surrounding area....feathered to the flaw. Scuff entire panel. Spray the area with matched paint (using a professional paint gun)....being sure to feather the pigment outward from the flaw. Color sand. Apply clear coat to entire panel. Polish with compound. Buff.
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