Tim Tebow has stated that he doesn't feel the political realm is for him at this time and would rather expend his energy in his charitable foundation. It is better that he stays true to his values and goals when he is asked to take a public or political stance.
Tim Tebow made he correct decision to turn down Donald Trump's offer to speak at the RNC. Tebow has strong religious beliefs, including anti-abortion views. This conflicts with Trump's previously stated pro choice statements. Tebow has to follow his conscience in deciding whether to speak at the convention and support the nominee.
I don't think that Tim Tebow was right or wrong to turn down Trump's RNC offer. IF he doesn't think he can support this candidate, then he definitely should not be speaking there. In addition, Tebow's fame has really decreased since his NFL failure, so I don't think people care about his opinions anyway.
Tim Tebow has the right to turn down Donald Trump's invitation to speak at the Republican National Convention. Tebow is the only one that can make the choice as to whether or not he will speak. If he does not want to talk at the convention, then it is his right to decline the invitation. In short, Tim Tebow made a personal choice when declining to speak at the RNC.