I think Dipping should take a full action as coating a weapon in poison in 5e takes a full action. And it should have some kind of duration, even if that duration is 10 rounds. Otherwise I think it is mostly fine, maybe for immersions sake to light a metal weapon on fire it will need some kind of oil or fuel applied to the sword before hand? While arrows it should be relatively free and if you ignite a wooden staff or club that might be a bad idea and so the weapon can be damaged if you don't put out the fire? Might add function to mending if it is ever added.
