Hello krkr,
have you tried it yet?
FieldX by default is saved in introtext field in the #__content table of your db.
I made a test content type with a test fieldx that uses a calendar field. Name of field is test_calx.
When I create content for it I can then search the DB for "test_calx".
It reveals one entry in table #__cck_core_fields and one intable #__content. In the #__content table in the introtext field SEBLOD stores the calendar fieldx values like this:
::cck::85::/cck::<br />::test_calx::2::/test_calx::<br /><br />::test_cal|0|test_calx::2013-09-29 10:35:00::/test_cal|0|test_calx::<br />::test_cal|1|test_calx::2013-09-29 10:35:00::/test_cal|1|test_calx::<br />
In the v2 documention for fieldX it says: "Please note, use only the storage "custom, Article, introtext" for the field "fieldX"."