I'm trying to import rrules for CCK datefield using Date API 5.x-2.x-dev

What format do they need to have? In the DB they are stored like this:
RRULE:FREQ=WEEKLY;COUNT=10;WKST=MO;BYDAY=TU,TH;UNTIL=20150101T000000

I tryed to map
myfield rrule (field_myfield) "RRULE:FREQ=WEEKLY;COUNT=10;WKST=MO;BYDAY=TU,TH;UNTIL=20150101T000000"

but import fails...
Thanks