I don't think that Trump did anything wrong by announcing his VP pick when he did. He needed to announce it before the Republican National Convention. He did show class by postponing the announcement once because of the horrible terrorist attack on Nice, France, so his timing was just fine.
Trump postponed his announcement for no reason. In a way I think that he is a bit scared, to do anything really. Which is a shame because so many people look up to him. I'd like for him to man up and get a little more comfortablem, take more chances.
Presidential candidates tend to announce their vice president picks in the days leading up to their party's convention. Therefore Donald Trump was right on time in announcing his choice for vice president. It's also helpful because announcing his choice enables voters to decide if they want the full package of Trump and Pence together, which influences their decision of who to vote for.
Donald Trump was right not to postpone his vice presidential pick, Indiana Governor, Mike Pence. Yes, there are a lot of major news events taking place all over the world. This might have preoccupied a lot of people that would have otherwise watched Trump's announcement. However, Trump has the right to chose the time for his vice presidential pick announcement.