I think you are a victim of Microsoft's woefully inadequate documentation. After a few tests I've come to the conclusion that when -t xx is referred to as a timeout for shutdown it means just that and it does not apply to log off.
You should also test the -f switch as that seems to do the exact opposite of what they say, i.e. with -l -f applications will not be closed automatically. Try it with Notepad and unsaved changes to see what I mean.
Alan.
Usage: shutdown [-i | -l | -s | -r | -a] [-f] [-m \\computername] [-t xx] [-c "comment"] [-d up:xx:yy]
No args Display this message (same as -?)
-i Display GUI interface, must be the first option
-l Log off (cannot be used with -m option)
-s Shutdown the computer
-r Shutdown and restart the computer
-a Abort a system shutdown
-m \\computername Remote computer to shutdown/restart/abort
-t xx Set timeout for shutdown to xx seconds
-c "comment" Shutdown comment (maximum of 127 characters)
-f Forces running applications to close without warning
-d [u][p]:xx:yy The reason code for the shutdown
u is the user code
p is a planned shutdown code
xx is the major reason code (positive integer less than 256)
yy is the minor reason code (positive integer less than 65536)
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