It's certainly open 24/7.
Occasionally they close one of the sides, you just have to use the other side.
Be careful at the corners; although it's always good to make sure you're able to stop within the distance you can see, be particularly mindful of it in the tunnel as you never know what you'll run into - anything from a sleeping ned lying in the mud to a left over beer bottle! A toot on a bell/horn can be a good idea.