You have plenty of water for watersport 2 hours before high tide and 2 hours after,you can stray out a bit more this time of year as there's not so much traffic.Regarding the slip no problems with a 4x4, if you haven't got a 4x4 there is a cable that you can use. As Phil said I launch my 7Mtr with a Suzuki Grand Vitara 2.5 without any problems at any state of the tide. The cable works very well allthough I have never used it myself, just hook one end on the trailer and the other over your towhook and have somebody guide the trailer down to start it off, once it starts going down it stays in the centre of the slipway, if you both have a mobile or two way radio it's easier as the slipway is steep and you can't see each other when it's down the bottom. There's not much weed down the centre of the slipway but it can get very slippery on the outside.
Have fun I may be down Sunday myself, If I am I would be happy to help you.