There is “dry,” and there is “cure”.  Cure is maximum hardness and takes weeks, always.

Consider:

Type of paint, temperature, humidity, and number of coats play a role in drying/curing.

Winter/summer and so on.

Thickness of the goop you painted, number of coats: you have to think about this. There’s no rule.

Before the second coat…

Many paints, stains, and varnishes have a “window” of time: you must recoat inside that window. If you recoat too soon, who knows the mess you’ll make. Too late, and you’ll likely have to sand the dry surface, then clean, then recoat. The horror.

Yes, read the label on the can, if you can still see it, for the info on re-coating time.

After the last coat…

BUT before you hang art or put objects on the new paint, think:  You can tear the paint if you place objects on uncured paint, and it sticks. Back to square one.

If you paint a shelf or cabinet, put paper or plastic under your items and move them all around every day for a few days as it cures. Then once per week. Cured paint is when it is totally hardened. This takes at least 2-4 weeks for latex house paint and more for oil-based coatings.

So plan it out.

Before painting, sand the shelf well, clean it well, then apply a high-bonding primer like Kilz or Bin.

PS: Dehumidifiers help.

Somewhat related reading:

The guy they paid to watch paint dry!

Related:

How Long to Wait Between Coats of Paint?

and

Cabinet Painting – Please Don’t Make This Mistake

Ask me anything below.