A sophisticated feature of the Blockstream Green wallet is its use of time-locked transactions. This is a safety mechanism built into its security model. If the Green service were ever unavailable to co-sign, after a predefined period, you could broadcast a transaction using only the key stored on your device. This feature guarantees that you can always recover your funds, providing an ultimate safety net against service dependency. The Blockstream Green wallet is designed for resilience and user empowerment in all scenarios.