With the default configuration, you should be able to sample up to 8 min. of CD quality audio into a track recorder (if you have not already sampled something else, in which case you must subtract from those 8 min.), because there is 80MB of RAM. This is from the classic document by Merlin, which is required reading for all OT owners and prospective owners:
http://elektron-users.com/index.php?option=com_docman&task=doc_download&gid=611&Itemid=30
Note that you sample into RAM, not directly into the CF card, although after you have recorded something into a recorder buffer, you will be allowed to save the buffer content into the CF card.