Extra Time (PAL - aka Better Translated Version :P) is a good mechanic for Ranked, and there are numerous reasons why it exists. There's no need to complain about it existing, and calling it bad or annoying because it causes you to lose. It exists so that the losing team has a reason to keep fighting, to prevent rage quits and to keep the matches competitive, close and exciting. If it wasn't there, people would rage quit dc most matches when it became clear they weren't going to win because they were in the last minute of the match without much luck pushing and knowing full well that the timer would end before they could take the lead. I just looked on Inkipedia for the information on how Extra Time triggers and works for the other modes and overall, it's a fair system (bar Tower, which has the hardest Extra Time for too many reasons).
Let's start off with Splat Zones, Extra Time will trigger if, and only if, the losing team has control of all zones ("You've secured all Splat Zones!"/"We're in control!"), if that hasn't been triggered, and the clock hits zero, boom, no Extra Time. When it is triggered, it'll end if the enemy team capture the zones, neutralise a zone and keep it so for 15 seconds or the losing team takes the lead. For this mode in particular, the losing team need to have their specials ready to help set up a final stand, to push the enemy back and stall the, away whilst the timer ticks closer to the lead. They need to be coordinated, set up a good defence, and close off all entrances to the zone. If they screw up, then it is their fault for losing, however it may not entirely be their fault in all matches. The winning team needs to keep their cool, survey the situation, and get in where they believe there's a weak spot in the defence to wipe them and take the zone. If they lose the lead, it's generally their fault for panicking, rushing in without thinking and getting splatted, being a detriment to the team. They need to take their time (but not too much, since they are time pressured for the lead) to ensure they can successfully break in and prevent the losing team from taking the lead.
Tower Control is the one that sucks in Extra Time for the losing team, as this only triggers if they're on the Tower, and ends when the Tower times out from them not being on it. This one sucks because the winning team only needs to Kraken, Bubble, Killer Wail or Inkstrike at the Tower, thereby forcing them off the Tower and allowing them to get on it, ending the losing team's chance of taking the lead. Of course, in the rare occasions where the losing team is close to their current distance they can do the opposite to force the other team away from the Tower to take the lead. All in all, this mode sucks for Extra Time, so you really need to get the lead early on and hold on to it, as it's easier to win as the leading team in Extra Time than it is to win as the losing team.
Rainmaker is more interesting though, and ever since I learnt how it worked has made things a lot easier to prevent Extra Time from ever triggering. Extra Time triggers if the losing team has the Rainmaker currently, or the leading team drops it in the last 15 seconds of the match. It will not trigger if no-one has been in control of the Rainmaker for the last 15 seconds, if the leading team is in possession as time hits 0 or the losing team drops it in the last 15 seconds. This Extra Time really focusses on teamwork, as the Rainmaker carrier becomes the biggest target since when they get splatted, the Extra Time period ends. So the other 3 teammates need to help protect the Rainmaker and assist in splatting the other team, to allow for a good push to take the lead. It requires the Rainmaker to also not make poor judgements, if they try anything too risky they can get splatted before their teammates could clear the way or assist, effectively throwing the match. If you're the team with the lead, don't pick up the Rainmaker unless it's on your side or you can successfully hide it in the last part of the match, or wait until the last 15 seconds is reached before splatting the Rainmaker, and stall out the shield as they aren't left with much time to pop the shield open and grab it.
Overall, you need to just keep calm, focussed and make the best possible judgements within each mode and each Extra Time. Working well as a team and being effective with your positioning and choices can be a big help in coming out victorious in Extra Time. A well timed special or sub can be so critical in the outcome of the match, and you need to make sure you do it right. If everyone on the team works together and keeps it cool and collected, Extra Time should rarely ever go wrong (unless you're playing Tower Control).