I have to agree 7-8 hours. You have 45,000 chips out. Rule of thumb is when the BB = 5-10% of the total outstanding chips, the tourney will end. So... you have to go a little farther in the Blinds.
Why would you want this tourney to last that long anyway? I would shot more to <3 hours for this.
Try the foxwoods blind schedule. It may help.
I just ran a tourney this weekend 30 players, 2000 starting chips, with some rebuys and addons, TOTAL OUT: 100,000 chips
Lasted for 6 hours with at least 30 minutes in breaks. Last level was 2000,4000. I used the Foxwoods schedule to a tee.
Scotty O
Click on the Blinds.xls link for a chart of the Time v. Total buyins using the Foxwoods schedule
http://www.geocities.com/thepokerfanatic/