In reply to Rob Laird:
Access windows vary on Springs and Neaps, but typically 3 cliffs is free of the briny stuff for 2 & a half to 3 hours either side of low water.
Not climbed on Yellow Wall (the other end of the difficulty scale) but judging by Mewslade and King Wall nearby (where I have climbed) I would expect a similar (perhaps slightly shorter) tidal window.