I think it would be until whenever the final day for acceptances is in August..although normally a counter bid would come earlier to avoid some shares going across to CS CSG.
We won't have documents until the regulators approve the deal (i'm guessing).
So there is alot of time here for a coutner bid , but I wonder if BG will risk doing anything to unsettle CNOOC given the links to CNPC/Petrochina