At maturity
From the maturity date, one PT can be redeemed for SY worth one unit of the accounting asset, and the SY for the underlying asset. The YT stops collecting yield; what it collected before the date can still be claimed.
Redemption has no deadline. A PT held past maturity keeps its claim but earns nothing more: its value in the accounting asset stays at one unit.
The way back to the base asset
Redeeming the PT returns SY, and unwrapping the SY returns the underlying asset. Turning the underlying into its base can take longer: a staked token may have an unbonding period, a savings token a cooldown, a fund a redemption queue. Maturity ends the price risk of the PT; it does not shorten those steps. Each asset page states what the issuer documents for them.
Rolling
A holder who wants fixed yield beyond the date can roll: redeem the matured PT and buy the PT of a later maturity on the same asset, where one exists. The new rate is that day's implied APY on the later market, which can be higher or lower than the old one. One of the research notes here measures what happened to that rate around past maturities.
LP positions and YT at maturity
An LP position in a matured market holds PT, now worth its full unit, and SY. Withdrawing it returns both, and the PT can then be redeemed. After maturity the YT itself is worth nothing. The yield and rewards it earned before the date stay claimable by the address that held it, and do not pass to whoever receives the token.
The calendar
The maturities page lists the dates of the live markets on the assets described here, by month, without rates.