Last 2-3 years I've fudged my FTP based on what I can do mainly in z3 and z4. 45 minutes is the longest I've had to hold a break neck pace; going an hour all out is hard. Unless its a TT, going all out for an hour probably means you're going to lose (or your competition sucks). I also know my zone settings are different compared to others; my lower zones (z1-z4) are better and my higher zones (z5-z7) are terrible; I both don't have much power over FTP and can't hold it as long. The Zone thing is not linear like it shows in the software like WKO, etc. My Zone 6 is probably 20% worse than other racers but I can hold threshold longer. A solid TT'er profile (I'd rather not have).
I've tried about 4 times outdoors to do a legit hour TT, each time something has went wrong. Sometimes its as simple as a car cutting you off, having to hit the brakes, and that lapse just kills it. On top of that, its just really hard mentally to go all out that long when nothing is on the line. Occasionally I'll do an all out 20 minute test because I want to break 300w (I've gotten close) and I'm really curious to see how I'll do after doing a year solid of base and tempo work only.