From LAMMPS Documentation:
"The Tdamp parameter is specified in time units and determines how rapidly
the temperature is relaxed. For example, a value of 100.0 means to relax the
temperature in a timespan of (roughly) 100 time units (tau or fmsec or psec
- see the units command). "
If You don't add a "drag" value to the fix nvt command, LAMMPS uses the
unchanged Nose/Hoover algorithm, therefore the tdamp value is the relaxation
time.
I am not sure what You mean with the "messages after #25". If You speak of
the emails from this mailing list, an archive is avaible at:
http://sourceforge.net/mailarchive/forum.php?forum_id=46682
I hope that helps,
best regards
Christian