I can find how soon mometamax will act, it only says “rapidly”.
If he’s eating and taking treats etc, I don’t think Reglan would be warranted, but if he’s very prone to stasis you’ll have to go by what your gut tells you. After all, you know him better than anyone. I have never used Reglan.
I wouldn’t use our emergency vets here unless a condition was life-threatening, I don’t really trust them to give the best care. If a rabbit is scratching his ears and I have the appropriate med at home, like you do, I’d try to keep my calm (which is not easy, believe me I know), trust the med I have and try to get the regular vet to fit him in on Monday. Unless he takes a turn for the worse, I doubt an emergency vet would do more than give him ear-drops, possibly an oral ab. But again, you know this little guy best and how to “read” him.
Keep him comfortably warm and see if he takes treats, try to distract him from itching (sometimes an itch is “fed” by the act of scratching it), maybe the corticosteroid will do it’s work meanwhile.