Hi tsots! I have to say, my absolute gut response is to say "when you KNOW you can do it and stick with it!" I know one girl at work who gets up at 5am every day so she can work out for an hour before showering and getting ready for work. I would just as soon die (well, maybe not QUITE) as get up that early! I'm definitely an afternoon person. I have to be careful when my workout happens right after work because I'll end up with my metabolism so revved that even 5 hours later it's hard to go to sleep--I try to save my really long workouts for Fridays and the weekend.
I'm not sure that I really buy into that whole business about limiting the amount of cardio or other exercise you do. My mantra is that your weight loss journey is a personal experiment of one. We can all give advice, but in the end, you will have to learn through some trial and error about what works for YOUR body. One of the reasons I absolutely HATED WW so many years ago is their rather rigid perceptions about exercise and adding points. Basically, you would think that WW was unaware of endurance type exercise. I'm actually preparing for a big event in 2006 that has me looking at weight loss as embedded within a larger training program and 30-60 minutes of aerobic exercise every session won't cut it. I have at least one session/week that is getting progressively longer (and will get up to 6 hours). I *do* add calories back in when I have long exercise sessions and that would be my main recommendation--learn your balance between calories consumed and your exercise level. If you decide to keep your long cardio sessions, then just adjust your intake to keep your body running smoothly.
Geez....I always write such long notes.....