"When are you going to Aberystwyth?"
Translation:Pryd dych chi'n mynd i Aberystwyth?
This was written by ibisc that you might find helpful:
Questions about how, when, where, why, how often, how quickly, etc, or which start with a preposition or an adverb are generally followed by mae - sut (how), pryd, ble/lle, pam, pa mor aml, pa mor gylfym, am beth, i bwy, gyda phwy, etc.
Am faint o'r gloch...? is asking when, so it is followed by mae.
Sut mae Dewi heddiw? - How is Dewi today? Pa mor aml mae e'n dod yma? - How often does he come here? Ble mae e'n eistedd? - Where does he sit? Gyda phwy mae e'n eistedd? - With whom does he sit? Â phwy mae e'n siarad? - Who is he speaking to? (With whom is he speaking?) I bwy mae'r anrheg? - Who is the present for? (For whom is the present?)