In reply to spenser:
> I haven't visited Ynys Lochtyn but if the crags on the island are none tidal it could be a good option, walk out in the morning, climb while cut off, walk back at low tide.
Hidden Wall on Ynys Lochtyn is non-tidal and has >30 climbs from D-E4 on immaculate hard sandstone (same as that on Carreg y Barcud, but generally blockier.) The extreme RHS of the wall - right of Dolphin - has numerous bouldering possibilities as well. All other cliffs on the island, or elsewhere in the area, are unfortunately tidal, but this doesn't matter as there's plenty to go at on Hidden Wall.
Access to Ynys Lochtyn is possible up to 2.5h either side of HT (neaps) by descending a steep path (or abseiling from an in situ BMC stake) and then crossing a short boulder beach to the island. As spenser rightly says, you can cross before HW, climb through the HW period and then leave on the receding tide once the beach is accessible once again. Being temporarily cut off on the island is guaranteed to provide considerable bemusement to walkers on the nearby headland! About a 45 mile, 70 min drive from St Davids, and definitely more adventurous/ memorable than the default 'drive to South Pembs/ Saddle Head' alternative. Probably well worth the extra effort for 1 weekend day.
I've climbed a lot in the St Davids area with HW in the early afternoon and have always, as others have already suggested, headed north onto the gabbro cliffs. Craig Coetan's already been mentioned. It's a good little crag but can suffer from seepage after prolonged wet weather. Nearby Mur Cenhinen is also non-tidal as are some other crags just to the north. Again better than the S. Pembs alternative IMHO, chiming with what others have already suggested.
HTH
Dave