Do they need the roof for the lights? If so, will they start closing the roof the moment this match is over? If they wait and do it later there will be a delay as it takes something like 30m and can't be done during play, iirc?
They do need the roof for the lights, but closing the roof once play has begun usually only results in ten minutes delay. When they decide to do it is anyone's guess, but will depend on when this marathon ends. If they can get the second Semi on by half-seven, my guess is they'll play for an hour or so with the roof open. Of course, if it rains in the meantime, the roof will come on, and stay on for the remainder.