Time clauses are used to indicate when an action occurs in relation to another action. They are introduced using time conjunctions such as when, while, as, before, after, since, till/until, as long as, as soon as, by the time, during, whenever, immediately, no sooner...than, the moment that. When the time clause precedes the main clause, it is separated by a comma. The present simple tense is used in time clauses that refer to the future. Care must be taken when using will after when as it can indicate a noun clause rather than a time clause.

1. TIME CLAUSES

2. These clauses broadly answer the
question
When?

3. The following time conjunctions are
used to introduce time clauses:
when, while, as, before, after, since,
till/untill, as long as, as soon as, by the
time, during, whenever,
immediately, no sooner…than, the
moment that, etc.

4. When the time clause precedes the
main clause, a comma is used.
Whenever he is in town, he visits us.
time clause main clause
He visits us whenever he is in town.
main clause time clause

5. Tenses
When the time clause refers to the
future, the present simple is used.
I will call you as soon as I get to my hotel.

6. Main clause Time clause
Present
Future Present Simple
Imperative
She takes off her shoes the moment that she
gets home.
I’ll tidy up after we finish cooking.
Lock the door when you live.

7. BE CAREFUL!
Will can be used after when in noun clauses.
I don't know when she will arrive.
I can't remember when the race will start.
In these sentences the question is: What? not When?

8. Awesome lines by Charlie Chaplin :
You need power only when you want to
do
something harmful, otherwise love is
enough to get everything done…