Nothing wrong with 80BB starting stack. With that structure it should last 3.5-4 hours. I would rather shorten the blind levels and have a smoother structure. Something like this with 20 minute levels would give you a smoother structure and the same amount of play:
Blind Structure
Level Small Blind Big Blind
1 25 50 -
2 50 100 -
3 75 150 -
4 100 200 -
5 150 300 -
6 200 400 -
7 300 600 -
8 400 800 -
9 600 1200 -
10 800 1600 -
11 1200 2400 -
12 2000 4000 -
Level Time = 20 minutes
Total Chips in Play = 80000
Starting Chips = 4000
Chip Distribution (per player)
8 x 25 chip(s)
8 x 100 chip(s)
6 x 500 chip(s)
View with Blind Valet