Counting all regular studio albums starting with When Dream and Day Unite, ending with Black Clouds and Silver Linings, no lives, no Greatest Hit, no bootlegs. Out of ACOS, just the title song is included. Counting Six Degrees of Inner Turbulence CD2 as 1 song, and In the Presence of Enemies also as 1 song.
The total playlist length is 12:37:29. There are 93 tracks. Subtract 7 for SDOIT and 1 for ITPOE. This is 45,449 seconds in 85 songs, which is 534.694118 seconds per song.
Thus: The average Dream Theater studio song is 8:55 long.
The average Dream Theater studio track would be 8:09.