There are too many variables to give you a clear answer. What kind of surface was the paint applied to? What kind of oil was the paint made with? What pigments are in the paint? How thick is the layer of paint? Did the manufacturer add anything to the paint to even out drying time between different paints? Did you add solvents or mediums to the paint? And so on.

Drying time can vary from a few hours to two or more weeks.

Sorry about the delay. Oil paintings (dry or wet) left in the dark for long periods tend to turn yellow. That happened a couple of months ago to a panel I had primed with lead white but not yet painted on. I left it partially behind another panel, so that part of if was in shadow and part of it not. The part in shadow turned yellow.

Fortunately, exposure to light fixes the problem. I left the panel completely out in the light for a few weeks and the yellowing disappeared.

The lights don’t have to be on all the time. Just a normal amount of room or sun light will prevent yellowing from happening.

I’d remove it from the radiator and let it dry at normal room temperature. But it will likely be OK.

I don’t know. I’ve never done much impasto in oil, so I haven’t experimented. I expect it would depend on exactly what the formulation of the glue was.

If you want really thick impasto without waiting a decade for the oil paint to dry, you might consider applying the first layer in acrylic. There are lots of additives for acrylic designed to make interesting impasto textures—if these are rough, they will improve the ability of oil paint to adhere. Once you have the right surface structure, go in on top with a thinner layer of oil paint.