[FIX] report: datetime already imported, differently

This rev. is related to 439cdb68.

The module datetime was already available in the reports,
and it was the entire datetime module that was imported,
not just the class.

This rev. is not recompatible with 439cdb68,
but there is no other choice, since other existing
reports might already expected the datetime module
and not the class

opw-640299