Block timestamp rules

Block timestamps are miner-supplied and only loosely constrained: a valid timestamp must be (1) strictly greater than the median timestamp of the previous 11 blocks ("median time past") and (2) no more than 2 hours ahead of the node's network-adjusted time. Within that window, miners choose freely — so timestamps are not precise clocks, and consecutive blocks can carry out-of-order times.

Nuance: The two rules bound timestamp manipulation enough to protect difficulty adjustment (miners cannot pretend blocks took much longer than reality without their blocks being rejected). BIP-113 moved lock-time semantics onto median time past to remove miner timestamp gaming from time-locked transactions.

Common misstatements:

• "Block timestamps record exactly when a block was mined." — They are miner-chosen values within a tolerance window of roughly ±2 hours.
• "Timestamps must always increase." — Only relative to the 11-block median; an individual block can carry an earlier timestamp than its parent.