hasn't occurred overnight

English as a Second Language English Vocabulary, Grammar and Idioms
1

Here: It goes to show that the transition of Russian fiction from Dostoevsky to its present state hasn’t occurred overnight.

In the above situation, the act of the possible occurring overnight must have been in the past, and it is a clear past time reference; should/can HASN’T OCCURRED change to DIDN’T OCCUR?

2

Both are possible,

3

Thanks.