Why not try TMX in very low light levels its wonderful and hardly suffers from reciprocity failure at all and the negs are excellent tonally.

Must try these hours long exposures, at night in the landscape, but I don't own a watch and it was bad enough with 4mins @ f45 10days ago. But then give or take the odd 1/4hr will make no apparent differance. on a 2 or 3 hour exposure