Prior to that date the Dutch bank's shares had been trading between the Barclay's bid and the RBS consortium's indicative offer.

FORBES: Magazine Article

That date also matters because it is when Dutch voters go to the polls.

ECONOMIST: The European Central Bank

Under Dutch regulatory rules, Barclays must make its official offer to ABN shareholders on or before July 23, though is still unclear whether Dutch regulators also require RBS publish its official bid before that date.

FORBES: Barclays Wins A Round In ABN Battle