SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

How long does the water continue to drip?

The water shouldn't stop flowing the moment the valve turns off. The water in the drip tubing will still be pressurized and will continue to flow out of the emitters until the pressure drops. Then you have to consider gravity. If the tubing is on a slope, the water in the tubing will continue flowing out the lowest level emmitter until much of the tubing is drained.

I agree with HKDK, it is probably just normal drainage.

One thing to consider is if the valve used is not passing a lot of water, it may have a tough time closing. There MUST BE BACKPRESSURE on a valve diaphragm or it won't close properly. Drip systems are well known for not closing down if there's less than a 1/4 gal per minute flowing thru' them.
Consider adjusting the flow control on the top of the valve if the dripping continues for much more than an hour or two at the lowest head.
You can also put a screwdriver to your ear with the business end on the valve to hear if it's weeping or not.