As you say, it will take time. The only way a viable third party will arise, however, is if it is grown from the ground up, growing new support and organization as it goes along.
It must start at the local level. Get third party candidates onto local county boards, state legislatures, and US Congressional seats. Then you can go for the big prize.
There's no use in trying to get a third party candidate elected President if we can't get one elected as dogcatcher, though.
Until third parties recognize that fact, they are wasting everyones' time.
In less than 7 years the GOP was established and had elected a POTUS. The GOP was formed from Dems, Whigs and third party voters. That was in the age of limited media. IOW a third party could be established and literally thriving within an election cycle.
The political leanings of this nation as any nation on earth can literally change over night.
The GOP needs the threat of the possibility of a third party to bring it back in line. Remember the words of Jerry Ford "Where else can they go" referring to Conservatives at the 2000 convention. Ford is the symptom of a problem. The problem of our elected in both the DEMs and the GOP is believing they are owed a vote strictly because of their party name. Both think they are not replaceable and use fearmongering tactics to scare voters into voting straight party tickets no matter how bad their candidates are. If someone wants my vote they can earn it.
They can go and start a third party and history even the GOP's own history says it can indeed be done and can be done rather quickly actually. The GOP leadership needs to be the one coming to Conservatives rather than telling Conservatives to shut up and vote for the sake of the party then be quiet for another 4-6 years depending on the office.
The GOP leadership better wake up and remember where the votes that got them into power came from. Otherwise they may find themselves Whiged out of office.