Depending on what kind of metal, maybe you should first use a metal primer. As for the gesso, 2 coats is the way to go. Apply the first coat, let dry thoroughly and then the second. You can even sand between coats depending on the surface you prefer. I always do 2 coats, and wait till it's completely dry. 24 hours seems a little long, but that will depend on climate.
Follow the directions as closely as possible. But, if it's dry to the touch, go for it!!! I hate waiting.

Ditto to the above, and I do two coats, but when possible I do one coat side to side and the second coat top to bottom. It can also be lightly sanded when dry.

And as paintergirl said, use a metal primer. It is like an adhesive and your finished work of art will not chip for scratch as easily.

I have also heard that if you use two coats of the same kind of wax used on wooden bowls, it gives you a harder surface. Sure leaves a pretty finish.

Nice to see you back!

Belle