You need to figure out the exact level that you need to start at so that you hit your target batch size at exactly 60 minutes.
I always do boils that are longer than 60 mins. Usually 90 minutes. I know with my equipment that as I soon as I hit 7.2 gallons in my kettle that I am 60 minutes from my 5.5 gallon goal. This way I can put my first hop addition in at 7.2 gallons in the kettle and just countdown to zero from there.
On Tap: 1. Kelly R. IPA, 2. Roter Hund Hefeweizen, 3. Bud Killer Blonde, 4. Red Dog Pale, 5. Roter Hund Oktoberfest, 6. Pumpkin Ale, 7. McRed's Stout (with new nitro system and stout tap,) Cream Soda, 8. ESB # 3, & 9. Ordinary Bitter.