I certainly understand the "lives" thing. I can't run a 6 hour tourney either.
But as I see it (YMMV) you are starting with T25,000 x 10 players = 250,000 chips
Rebuys (unlimited) average 4 (again YMMV). 100,000 (total 350,000)
Add-ons; I've only known the nittiest op players to skip an add-on. Both home and casino play you are getting 90-100% add-ons. Let's say you only get 80% to add-on (you do refer to them as nits on the structure). +200,000 more chips for 550,000 on the table.
Level 12 (3000 - 6000) You have 91+ BB on the table. You probably have 5-6 players still in the game, with ~16BB on average. In a home game this is just starting to get into the jam/fold after the flop zone, but you can pick your spot and see a flop. It's also close to the money in a 10 player tournament, so short stacks may tighten up a touch to preserve their fold equity.
You then got from a 20% jump to a 60% jump to a 100% jump
with shorter levels! This is the meat and potatoes of tournament play. Who gets paid? Lets flip (or chop).
There are various ways to remedy this, including taking time 3-5 minutes off the 20 minute levels and adding both a 4000/8000 and a 7000/14,000. You could also reduce stack sizes, limit rebuys, make rebuys surrenders, or eliminate the add-on - but that sudden climb when just before the money is a casino-built "ok, did you guys want to chop" format.