Davy's Gray/ Davey's Gray. Oil color. How fast does it dry? Is it safe to use in my underpainting?

Oils are not like Acrylics it can't be rushed. Anytime you use and paint as an under painting it should be applied in thin layers...turpentine or thinner should help. I find it you are painting in a pre primed canvas drying time may take a little longer, because of the coated finish. It best to buy canvas that have a matt finish or prime it yourself. The matt finish will allow the paint to absorb into the prime surface quickly therefore allowing it to dry faster.