Present perfect

1. Raman hopes to become a professional after he finishes his Graduation.

2. She came to class much early than I expected.

This Are questions of tense from A grammar book.

1st question is written in the simple present, but it is wrong and the second part after
"after" should be written in present perfect i.e, it should be " he has finished his graduation"
the reason given is that the second action i.e. Graduation must be finished to accomplish
the first action, it is convincing but also confusing.
Present perfect is defined as an action that is started in near future and
finished in near present or has a relevence to present.
There are certain rules like usage of since, for etc to identify when to use perfect
tense but it is not possible for me to identify such sentences where I should go for
present perfect and not simple past or present.
When I read the statments , I thought it would be " after he finished his graduation".
Also, for the second statment than I expected should be written as than I had expected.
It is very confusing, can anyone please clear it and point out the mistakes I'm making to understand such statements?
Thank you!