It's essentially the same as buying and selling a house. Once an offer is accepted the buyers solicitor will carry out all the required searches and only after then, assuming everything is satisfactory do you formally agree to the sale and exchange contracts. In City's case, the accepted the offer on the 1st September, Abu Dhabi carried out their due diligence which was completed on the 21st and then the sale went through on the 23rd. As I said, it is possible that the PL began their checks prior to the 21st however that's still at most half the time it's taken for this deal to go through.