Ok, I trained up Discord to 120, and working on a 2nd character. With Music at 120 and using Tribulation mastery, Discord gains about 0.3/hour. Not fast, but it's progressing.
With Music at 100, Discord seems to be raising closer to 0.9/hour. So I think I'd keep Music at 100 until all the training is done, or at least until you're on the last 5 points of gaining Discord, then finally turn Music back up.