Verses with the word instant in the Old Testament (4 verses):

Isaiah 29:5
Moreover the multitude of thy strangers shall be like small dust, and the multitude of the terrible ones shall be as chaff that passeth away: yea, it shall be at an instant suddenly.

Isaiah 30:13
Therefore this iniquity shall be to you as a breach ready to fall, swelling out in a high wall, whose breaking cometh suddenly at an instant.

Jeremiah 18:7
At what instant I shall speak concerning a nation, and concerning a kingdom, to pluck up, and to pull down, and to destroy it;

Jeremiah 18:9
And at what instant I shall speak concerning a nation, and concerning a kingdom, to build and to plant it;