Do you wonder why the "Daily" quest ransack is on an 18 hour timer and not a 24??? Because a 30 minute quest would have to be pushed back 30 minutes each day. Eventually that quest would fall out of your play time. They made it an 18 hour timer so that you can have nice 6 hour window to rerun the quest "the next day". It's just common sense.
Yes, the "Weekly" roll either needs to reset on zero hour every week, OR have a 150 hour timer. It seems to me that this was just an oversight (seeing as they DID already consider this problem with Dailies). It should be fixed.