As you can see from the conflicting personal anecdotes, it depends on you. You're going to need to experiment and find out what works for you. Also, what is your purpose in riding and how does this effect it?
For me, my objectives are performance oriented. I can ride hard (race, training, whatever) for up to 2-1/2 hours without eating prior utilizing my blood glycogen stores (I suppose I could last longer if I went slower, but I haven't tried it). In fact, I have found that if I eat closer than 3-hours to my start, I can bonk badly. (Haven't figured out a physiological explanation, but I figure it has something to do with: eating "turns on" my digestive "engine" and convinces my body to get its energy needs from there. If I don't keep it coming, my body begins to shut down thinking I don't have any more.)
If I know I will be riding longer than that, I will take food with me and start eating it after the first hour. I aim for about 200-400kcals/hr--any more and it sits in my stomach and makes me feel poor. This equates to 2-3 gels (110kcals/ea). This is entirely inadequate for my cycling energy needs (900-1,000kcals/hr). Hence, why I can bonk if my system relies entirely on energy from what I eat. As opposed to relying on what I have stored (blood glycogen, at stores, or muscle stores).