bugged probably, I've heard that it closed for 20mins and opened again 4h 30mins ago, so next closing in 7h and 30mins...
when tiat is killed 10 times sod closes for 12 hour, on 12th hour (and while sod is closed) tiat and his minions spawns again inside the fortress and he is running to throne room. At this time IF a party kills him within 30 minutes from his spawn, sod closes again for another 12 hours, if not sod opens for the instance. This respawn is the aka "Mini Tiat"
now probably this 20 minutes you said was th "Mini Tiat" that has been killed so sod will stay closed for another 12 hours (normally this should happen)
As for the fast closing of sod i think that its possible because at this time of server its easy for clans to make 2 or even 3 CCs to kill tiat so i think it is easy to kill tiat 10 times maybe even in one single day
it opened in some hours after I replied so it wasnt opened for another 12hrs (open = ecs, closed = tiat)
someday there was SOD Attack in Progress, it went to SOD Conquest Complete so I entered as probably first person, went to ECS room and didnt saw any Energy Seed, I've opened map again and SOD went to Defense in Progress Stage, after some minutes I've got teleported out and SOD went to Attack in Progress Stage.
so that what you said, the Defense SOD (when you have to protect "something" from your mobs and "mini tiat") can be enabled on 10th tiat when SOD is in Attack in progress stage, if they FAIL defense, SOD will be Attack in progress again.
then, there is no way that in 20mins when SOD was in Attack in progress, 10 Command channels did Tiat...
/lf confirm because Lineage2 website uses forgotten language with explaining what does SOD Defense in progress mean.