Logging Hold-after-answer time during queued calls

I have an application where I need to report on the time a caller into a queue is put on hold AFTER an agent has picked up the call (to distinguish true-talk ACD time). I see in the log that there are entries created for starting and stopping hold music, but nothing in either the CDR or queue_log. Is anybody aware of a switch/setting/trick that will put this information into one of those databases, or possibly into another file that I can test when creating my report?