The ECB's Emergency Liquidity Assistance to Greek banks is the only thing that keeps the Greek banking sector alive amid huge daily outflows of deposits.
Savers pull out cash fearing a failure of the negotiations that could end in Greece leaving the euro.
The new review time for the amount of funding available to Greek banks via the ELA on Monday is timed to put more pressure on the Greek left-wing government of Alexis Tsipras to agree at the euro zone summit to reforms, without which the country will not get more loans from the euro zone and will default.