It's maturity is ideally the date listed in the contract (i.e. by Jan 9th) but may extend for 10 days in case a report's publication was delayed.
That said, you can sell contracts to other users (which is typically what happens ...) so when people buy a Yes contract for 5c they're not buying from Polymarket; they're buying it from somebody else. This allows you to make money before maturity. The reason for this is that you can mint YES+NO contracts by paying Polymarket $1 which nets you 0$ as you spent $1 and between the Yes and No contracts Polymarket pays back $1. But if you spend $1 for a YES+NO and sell the No for 50c to another user and the Yes for 70c then you net 20c or alternatively you sell the No for 5c to another user and hold the Yes to maturity and get the $1 back from Polymarket.
Although to be clear, I don't exactly know all the inner workings of Polymarket so it could be the case that they've started to act more like a House than a Market and they're actually putting money on the other side of the contract (IIRC, Kalshi is starting to do that for Sports-based contracts either that or having a partner company do it as opposed to actual users).
So for an example contract "Trump invokes War Powers against Venezuela by...?" - https://polymarket.com/event/trump-invokes-war-powers-agains...
It's maturity is ideally the date listed in the contract (i.e. by Jan 9th) but may extend for 10 days in case a report's publication was delayed.
That said, you can sell contracts to other users (which is typically what happens ...) so when people buy a Yes contract for 5c they're not buying from Polymarket; they're buying it from somebody else. This allows you to make money before maturity. The reason for this is that you can mint YES+NO contracts by paying Polymarket $1 which nets you 0$ as you spent $1 and between the Yes and No contracts Polymarket pays back $1. But if you spend $1 for a YES+NO and sell the No for 50c to another user and the Yes for 70c then you net 20c or alternatively you sell the No for 5c to another user and hold the Yes to maturity and get the $1 back from Polymarket.
Although to be clear, I don't exactly know all the inner workings of Polymarket so it could be the case that they've started to act more like a House than a Market and they're actually putting money on the other side of the contract (IIRC, Kalshi is starting to do that for Sports-based contracts either that or having a partner company do it as opposed to actual users).