Well I went and looked at the gnmidi set of utilities, and there is a way to do it, with the free utility mididir.exe. It runs under wine like this:

 wine -- mididir.exe -length
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That will give a print out like this for each midi file in the directory:

Y:\ZLIG~MY.MID:  (33 kb, format 1, 11 tracks, GS, 3:00)
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Where the MM::SS is at the end after GS,

Now you have 2 problems, working out a way to translate the crappy 8.3 notation output for the filename to the real filename, and extracting the MM::SS info and probably throwing it in a hash for saving in a database.

Heres an UPDATE: If you go to the free utilities section of gnmidi.com, there is the miditime utility. You can run it on an individual file like this:

#!/usr/bin/perl
my $midifile = shift;
system("wine -- midifade -songtime $midifile");
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and you will get output like this

song: units 0 -  34475   time 0:00.000000 - 2:59.545800
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So run it with backticks, and grab the last set of digits.