I believe if you have an OSSI terminal type then the timeout is 2 minutes, but other terminal types (vt220, w2ktt, 4425, 513, etc) the timeout appears to be 15 minutes of no activity for "list trace".
===============================================
list trace ...
LIST TRACE
time data
21:17:14 0 0 TRACE TIMED OUT
21:17:14 0 0 TRACE COMPLETE cid 0
===============================================
Hope this helps