The field definitions for CMR are in the same document as CDR field definitions:
http://www.cisco.com/univercd/cc/td/doc/product/voice/vpdd/cdd/4_2/4_2_1/cdr421.htm#wp34650
Guides for other CallManager versions can be found here:
http://www.cisco.com/univercd/cc/td/doc/product/voice/vpdd/cdd/
Just check out the Call Detail Record Definition document for the particular version of CallManager that you are interested in.
The dateTimeStamp field of CMR is in the same format as the timestamp fields from CDR (such as dateTimeOrigination, dateTimeConnect) etc, so you can search on that field, and the directoryNumber field contains the extension that the CMR record is for. You can relate the CDR and CMR using the globalCallID_callManagerId and globalCallID_callId fields though you may want to use the timestamp fields as well if you need to be exact, since those fields are reset when CallManager resets, so they aren't unique within the table/database.