I'm used to opening credits on TV shows being relatively short. HBO's Westworld series has an opening credit sequence that is 1 minute, 40 seconds long. Is that the longest opening credit sequence for a TV series, or is there a series with a longer credit sequence at the start of every episode?
The longest opening title sequence appears to be the Iranian TV show Zire Tigh at 3 minutes 21 seconds!
The longest English-language title sequence I can find is Twin Peaks at about 2 minutes 36 seconds (thanks to Walt for pointing it out in the comments).
Note that there are shorter versions of this opening as well (perhaps for syndication?) such as this 1 minute 36 second version on CBS' official YouTube channel.