If the judge has given the 'majority direction' that the jury not having reached a unanimous verdict, they should endeavour to reach one, but, if they cannot, the judge will now accept a majority verdict, the judge is obliged to accept a majority verdict,, a verdict upon which at least ten of them (with a jury of 12) are agreed. He cannot refuse to accept one then.
When the judge gives that direction is a matter for the judge himself, which he makes according to the length and complexity of the case and from observing and hearing what the jury says, through the foreman in open court, when asked whether they are unanimous, and he also gets clues from the kind of questions the jury ask and what is said when asked whether there is any part of the law or evidence about which they wish to have further assistance. There is a minimum time of two hours in all cases to which is added time for the jury to assemble in court and withdraw again.
Guessing when a jury will return with a verdict is a dark art but the practice of counsel running a sweepstake on the time, with money changing hands in open court, has been judicially discouraged ! (The money now changes hands outside the courtroom).