[douglas]

This doesn't look good for you. In this case, both the warp opener and the fleet will move on the same day with order determined by ship ID. Unfortunately for you, the enemy has a much lower player number and very likely has a ship in the fleet with a lower ID than your warp closer. If he does, his entire fleet will get to move through the warp point before you close it. Determining whether his fleet has a lower ID ship in it may not be possible, but examination of movement logs is your best bet (the order ships are shown moving when they move on the same day is what you'd have to look for); it's probably not worth the effort, though. I would say, go ahead and try to close the warp point ahead of his fleet, but don't assume he won't make it through in time. It is possible you'll cut him off, and you will at least block reinforcements, but plan for the worst. Whatever happens, though, you can at least be confident of saving the warp closer because combat doesn't happen until after all ship movement. If you have one available, sending a star destroyer to the star in that system would be a great contingency plan.

Edit: Oops, I forgot that warp closing can't be done in the presence of an enemy. If you try to close the warp point and it doesn't happen in time, the closing attempt will fail and the rest of the ship's orders will be cancelled. So, you can either try to close the warp point, hope it works (probably not a good bet), and risk losing the warp closer, or you can not even try to close the warp point and be sure of keeping your ship.