There are roughly 617 episodes of startrek each an hour long.(including comercials). So 617 hours. Typically speaking a TV show is 45 minutes without comercials so it take a little over 470 hours to watch them all
You need to go back and count the episodes again. There are 79 episodes of the original series each approximately 50 minutes long plus the original pilot. Then they had the animated series which has 22 episodes each roughly 24 minutes long. After that came the live actions sequels Next Generation 178 episodes, Deep Space Nine 176 episodes, Voyager 172 episodes, and Enterprise 98 episodes all 45 minutes per episode. That comes out to over 700 total episodes with a run time of over 540 hours.