A time clause is a dependent clause that begins with a “time word” (when, after, as soon as, etc.). Time clauses follow their own special rules for tense combinations. Therefore, the correct verb tense in a time clause may be different from what you expect.
Future Time Clauses
A future time clause uses the simple present or present perfect, with the simple present generally being preferred:
The meeting will begin as soon as everyone arrives. (simple present, preferred)
The meeting will begin as soon as everyone has arrived. (present perfect)
Do not use will or be going to in future time clauses:
We will go out for dinner after the meeting will be over. (INCORRECT)
We will go out for dinner after the meeting is over. (CORRECT)
I am going to review the file before I am going to meet with the client. (INCORRECT)
I am going to review the file before I meet with the new client. (CORRECT)
Past Time Clauses with “Before” or “After”
When before or after is the time word, you can use two simple past verbs in a sentence that would normally require one past perfect verb and one simple past verb. The past perfect is not required because the inclusion of before or after makes the difference in times clear:
Rick’s daughter locked herself in her room after he had grounded her. (past perfect)
Rick’s daughter locked herself in her room after he grounded her. (simple past)
She had stayed in her room for two days before she finally emerged. (past perfect)
She stayed in her room for two days before she finally emerged. (simple past)
Time Clauses with “Since”
When a time clause begins with since, the verb can be in either the present perfect or the simple past tense.
When the time clause action ended in the past, use simple tense:
Rick hasn’t spoken to Emily since he grounded her last week.
When the time action began in the past but continues into the future, use present perfect:
Emily hasn’t spoken to her friends since she’s been grounded.