no sooner than . equals to "as soon as..."
eg:No sooner was the frost off the ground than the work began.
地上的霜一消散,人们就开始工作了.
hardly when
Hardly had the thief seen the policeman when he ran away.
= Scarcely had the thief seen the policeman before he ran away.
=No sooner had the thief seen the policeman than he ran away.
=As soon as the thief saw the policeman, he ran away.
=Upon seeing the policeman, the thief ran away.