An adverb clause is a subordinate clause. It must be attached to a main clause. Adverb clauses of time are introduced by the subordinating conjunctions while, after, whenever, before, since, as, till, until etc.
While you were playing I was working.
Don’t use the cell phone while you are driving.
As I was walking down the street, I saw James driving a Porsche.
He went to work after he fed the cats.
He went abroad after he finished his studies.
After you have finished your work, you may go home.
Don’t talk while she is singing.
Do it before you forget.
Bring me some water before you go.
I have not been keeping well since I returned from Kerala.
Everyone rose to their feet when he walked into the room.
They were told to wait till the signal was given.
I will wait here until you arrive.
Whenever I go to London, I try to see Mathew.
Whenever I see him, I feel nervous.
As soon as he heard the news, he called me.
Just as he entered the room the clock struck.
No sooner did he see us than he disappeared.
An adverb clause can come before or after the main clause. When it comes at the beginning it is usually separated with a comma.