Matthew 25:6

‘But in the middle of the night there is a cry, “Behold, the bridegroom! Come you forth to meet him.” '

And then while they slept the moment that they had been awaiting arrived. In the middle of the night (not necessarily midnight, but possibly even later) the cry went out, ‘the Bridegroom is coming! Come out and meet Him'. None had known when He would come, and the middle of the night was an unusual hour. He had come at a time when they did not expect (compare Matthew 24:50). And that was when their readiness would be tested.