Clauses of time are introduced by 'Before, after, when, whenever, while, as soon as etc.'

'Tense use' in adverb clauses telling time.

I. Present Aspect

1.1 Present simple tense, present simple tense or future simple tense:

When John meets Sally, he greets her politely.

When John meets Sally, he will greet her politely.

The use of present simple tense in both clauses indicates that the action of greeting with politeness happens every time John sees Sally.

Note that '*When John will meet Sally, he will greet her politely'. is unacceptable.

Even though the action does not take place at the moment of speaking, it does not make any sense to use future simple in both clauses.

1.2 Present perfect tense, future simple tense:

Once we have talked with the management, we will proceed with the project.

When John has finished his report, he will go to see the film with us.

The writer wants to give a clear idea that the action in the main clause can happen only when the report is complete.

II. Past Aspect:

2.1 Past simple tense, past simple tense or past future simple tense:

After John finished breakfast, he read the morning paper.

John had his bloodmary as soon as he got up.

The use of past simple tense indicates the actions/events that happened in the past. (John does not behave that way anymore).

Before John went to class, he would drop by his grandmother's.

2.2 Past simple tense, past progressive tense: When and while are possible connectors here.

While Anna was unpacking, John was getting the photo developed.

Two actions were happening at the same time.

Somporn called to Manoon on his cellphone while/when Manoon was studying EG 221.

Manoon began his studying before and until Somporn called him.

***The action which is expressed with past progressive tense does not necessarily a longer action. For example:

When John was bending down to switch off the TV, he hurt his back.

2.3 Past perfect tense, past simple tense:

Before John married to Sally, he had set up his own small business.

After John had been successful at his career, he thought about settling down with someone, so he got married to Sally.

By using 2.3 tense pattern the writer wants to explicitly show that one action happened and ended before the other action happened.

Should the writer use 2.1, he simply wanted to say that there were two actions.