You can try this, though I'm not sure the tag() function works during import:
On the AutoImport settings there's a section to define Tags to set during import. Click on Add, select the "Date (Release)" field, and set it to this expression:
convertdate(tag(RELEASETIME))
The timestamps you describe are UTC timestamps. If you want to correct them to your timezone just replace the red part with your offset in hours:
Math(convertdate(tag(RELEASETIME))+2/24)
You can use the same expression to quickly set the field on already-imported files using the Tag panel.