Scheduled (Delayed) Transaction Broadcast

The concept of nLockTime within Bitcoin transactions presents a nuanced challenge in terms of privacy and scheduling. nLockTime is designed to specify the earliest time a transaction can be added to the blockchain, which, theoretically, could enhance privacy by obfuscating the actual time a transaction was initiated. However, the implementation in Bitcoin Core reveals that there's an inherent trade-off. A significant portion (90%) of transactions with nLockTime set reflect the true block height at the time of their creation. This makes it relatively straightforward to deduce that a transaction with an nLockTime older than approximately 17 hours was intentionally delayed, thereby leaking information about the transaction timing.

Moreover, Bitcoin Core employs a specific strategy where there's a 10% chance that a transaction’s nLockTime is randomly assigned a value within 100 blocks of the current height. This approach, known as DiscourageFeeSniping, aims to mitigate certain economic attacks but also complicates the use of nLockTime for privacy or scheduling purposes.

For users interested in leveraging nLockTime for scheduling transactions at a specific block height, the process is not straightforward. The primary tools available for this purpose, createrawtransaction and walletcreatefundedpsbt, do not seamlessly integrate nLockTime settings into most transaction creation workflows. This limitation signifies a gap in functionality for those who might benefit from more granular control over transaction timing without resorting to less efficient methods like using a simple sleep function before sending a transaction via command line.

The potential for enhancing Bitcoin's transaction scheduling capabilities lies in simplifying the process of setting nLockTime and enabling transactions to be sent based on block height rather than or in addition to specific times. Such improvements could offer users greater flexibility and precision in managing their transactions, aligning with broader needs for efficiency and privacy in digital currency operations.