Mine last 1 hour to 1.5 hours.
Yes, your test level declines after 45 minutes, but that occures whether or not you continue training. So it doesn't matter if you leave or not after that point.
A lot of good programs just plain need at least an hour, if you are taking adequate brakes. The 5x5, JS's old program, Metal Militia, etc.
However, some great programs can be busted out in 45 minutes or less, like HST or WSB (however, my WSB program takes 1.5 hours).
Don't be too concerned with how long a program takes you. As long as its a good program, and your rest periods between sets are 1-5 minutes (unless otherwise noted) you are totally fine. Its really not a big issue at all.