YES! This generation's fans want instant gratification. They get that with satellite and cable TV, and the internet, email, chat rooms, text messaging, etc. They have short attention spans, very little patience, and are bored very easily.
Being a successful main eventer in a huge company like the WWE (and TNA, as well) is extremely difficult. The pressure is incredible. Not only do you need the in-ring abililty, but you have to connect with the fans (either as a credible and believable heel or as a credible and believable face), and you have to be able to speak to large groups of people hanging on your every word. There are no "CUT! Let's try it again" retakes. They have to get it right, every time. Those groups of people are looking for you to screw up. They WANT you to fail (whether or not they will admit it). You have to prove to them that you ARE worthy of their attention and emotions, of being a main eventer. You can't just walk out there with a "cool" gimmick and be an instant success. Most wrestlers (in the WWE, at least) who get that main event push don't last long at that level, even experienced veterans. The real main eventers (Edge, Triple H, Cena, Kurt Angle, Booker T, etc.), the ones who have proven they have what it takes to "carry" an event, a show, even a promotion, get picked apart by the fans.
A great example is Kozlov. A 300-pounder who has a lot of wrestling skills, but not a "flashy" gimmick. Deemed "unworthy" of main events by a large portion of the wrestling fans, he is crucified by his detractors who never gave him a chance. As soon as he got to the Triple H / Undertaker level the fans lit into him without giving him a chance to learn from the main eventers, after engaging in months of squash matches. Wrestling the main eventers, his weaknesses were exposed, and the fans just wrote him off as a "botcher", never giving him a chance to improve.
Evan Bourne. A spectacular cruiserweight; most fans want him in main events and championship pictures. Realistically, though, he's too small to be a believable World Champion. Rey Mysterio has a lot of fans. Rey is a spectacular cruiserweight, as well, but few consider it believable that he can regularly beat guys 100+ pounds larger than he.
BQ: There is no set time frame. A wrestler has to have "it", that intangible something that sets him apart. Randy Orton has "it", John Cena, as well. It took Jeff Hardy a decade to get there, Matt Hardy still isn't there. The Undertaker was a main eventer almost from day one. Hulk Hogan WAS a main eventer from day one.
For some, it's finding the right gimmick. Steve Austin and Rocky Maivia are two prime examples. Chris Jericho and Mick Foley are, as well. They were all potential superstar main eventers who just needed the right gimmick.