I could give you a NOT RECOMMENDED tip on how to increase the smelter-speed, but you could use ''sleep'', after using ''devcommands'' in the dev-console. As I said, NOT RECOMMENDED. (especially not in Multiplayer, unless the Members of the server agree.) What does the command ''sleep''? Not much to explain, it just skips the night, or day, if you feel like putting the command in daytime for some reason.