I don't think there's any point in attempting to rely on what a tidal watch is going to tell you. There's no such thing as accurate tidal predictions unfortunately. There are far too many factors at play apart from the predictable astronomical ones - wind direction and strength, atmospheric pressure and even recent rainfall. Our club spends a lot of money on expensive tidal prediction software which can - in theory - give a tidal height for any 10 minute point. Sailing on a tidal river estuary (the Firth of Forth in Scotland) and using a slipway that needs 1.4m over chart datum for us to be able to use it means that knowing when low tide is (and how low it will be) is important to us in scheduling racing. However experience tells us that the best tidal prediction can be out by 2 hours or more.