[asterisk-users] conversation record prematurely

[Joseph]

I have following line in a context:

...
exten => _587NXXXXXX,n,Set(recordfilename=${CALLERID(num)}-${EXTEN}-${STRFTIME(${EPOCH},MST,%C%y-%m-%d-%H%M)}.wav)
exten => _587NXXXXXX,n,MixMonitor(${recordfilename},b)
...

It records the conversation but it ends prematurely, after 10min. Why?
Where is the setting to records until a user hangup the handset.

-- 
Joseph