Dwy funud (or more colloquially Dwy funed) is like saying "Just a sec" or "Hang on".
I guess so. Though for "One moment" there'd be a few translations: Dwy funud, Un funud, Hanner munud, Un eiliad, Aros funud, Arhoswch eiliad etc.
So chances are that you're helped faster when you hear dwy funed than when you hear mewn munud? :)
Ah no, sorry, muned is only colloquial in south(west?) Wales. Otherwise you’re good to go with munud.