I assume Richard means the actual crossing to the island, which is indeed under water at high tide. Next Sunday low tide is 15.20 and high is 21.00; so by Tuesday about 17.30 and 23.00. I'd guess this will be fine for getting onto the island, and even coming off after sunset (which is about 18.40). You can always wade - from the otiose little shelter on the south side of the island, walk a curve that keeps you just to the south of the rocks that mark the shallowest route. The tides next week are big ones, though, so careful!