There are two markets on Polymarket about when Iran's Supreme Leader will take office. One is <by> and the other is <on>. 'By' means any day before the date counts as Yes, while 'On' is specific to the exact day. Iran has just made the final decision on the Supreme Leader candidate, and the likelihood of an announcement on March 8th has surged. It might be announced as early as Monday, but if you want to play it safe, you can also buy into the 'By' market for a few days later.