At what block height may locktimed transactions get included?
A transaction becomes valid when the chaintip reaches the height specified in the locktime, and may be included in any block with a height greater than nLockTime.


    if ((int64_t)tx.nLockTime &lt; ((int64_t)tx.nLockTime &lt; LOCKTIME_THRESHOLD ? (int64_t)nBlockHeight : nBlockTime))
    return true; 

  
  via https://github.com/bitcoin/bitcoin/blob/v0.19.0.1/src/consensus/tx_verify.cpp#L21L22


H/T Pieter Wuille for code section and explanation.