Translation:Are you going to Aberdaron on Friday morning?
As I understand it, the dydd is included when talking about days to avoid confusion between dydd Mawrth (Tuesday) and mis Mawrth (March). For similar reasons, the mis is included to avoid confusion between mis Hydref (October) and Hydref (Autumn). However, as Jehra2 stated, if you are talking about a particular time of day, e.g. bore Mawrth, prynhawn Gwener, you can leave out the dydd. That's only my understanding of it though.
I didn't realise mis Hydref and Hydref were different things (October is in autumn anyway so makes sense in that way). That's helpful to know. I have noticed that when referring to days of the week singularly it is written 'dydd Llun' but have four D's when inserted in sentences especially queries, like this 'ddydd Sul' etc.