Hi Andrew,
The AA route says about 30 mins. That is about right.
Mike123 Bristol to Magor Services
tenerifemike Magor Services to Junction 33 Cardiff
30 mins
48rov06 Junction 33 Cardiff to Swansea
eurorover Swansea to Carmarthen
thorfrun Carmarthen to Haverfordwest
Haxx Haverfordwest to Eglwyswrw (via Fishguard)
Dragrad Eglwyswrw to Aberystwyth 1 hour
Mike