People rarely discuss that batting a little longer can actually make you more attacking. It sounds like a contradiction but bear with me.
If we declare overnight and pakistan make a good chance then cook will start to push the field back because scoring just over 300 in a day is not that hard in the modern game. Imagine a big drive sees an edge and the ball goes through third slip at a catchable height to be picked up for a single at third man. If we declare now this could happen quite early but if we attack for one hour to score 70 runs then we can keep the catchers in because the runs are less important.
Personally I reckon that Pakistan are very skittleable which is not a word but you know what I mean.
Think 300 would be very difficult in a day if a fielding team went properly defensive. No field restrictions and can bowl leg side and wider (and slow the over rate down), so very easy to restrict scoring if necessary - you're right, a slightly larger total takes the loss out of the equation, but it also increases the likelihood that the oppo won't go for it and will try to block out. The attacking option is to give them a fighting chance, but where they'll have to take risks to go for it - the overnight declaration will do that but can't see it happening. 30-60 mins this morning, declaring at 350 ahead or when Bairstow gets his 100 if quicker perhaps.