The Bitcoin transaction lock time is the time when a particular deal can be added to the blockchain. This is the earliest time that miners could solve Merkle’s computing to attach the deal information to the latest block of the blockchain.
There are two types of transaction lock time. First, when the lock time figure is less than 500 million, it will be interpreted as a block height and miners need to wait until the block height reached at least 500 million to put it in a block.
Second, if it is more than 500 million, it will be converted to a Unix timestamp – a Unix timestamp being the number of seconds since January 1st, 1970.