Migration again

In my search for speed gains in migrating data from MSAccess to PG, I
postponed the creation of indexes (except unique indexes) until after data
import.
Now I'm thinking of postponing data validations. I'm thinking of validation
checks across multiple columns or even tables e.g. creationdate <=
lastchangedate.
As redesigning the migration procedure would take me quite some time, I'd
like to know if I should expect significant time savings overall by
postponing the checks until after data import.
Thank you all.

P.S. I wanted to implement the suggestion to group all inserts in one
transaction, but I could not figure out how to do it from MSAccess :-(