If I undestend the your question, you referer to the lockTime inside the transaction and not the block timestamp.
The lockTime is a int value, and this value rappresent "When the transaction can be unlockd to an inputs" and not "When the transaction was published"
Lock time: Defines the first instant in which the transaction is considered valid and can be transmitted on the Bitcoin network, represented by an integer value between 0 and 500 million, assuming different meanings based on the value assigned, that is:
- Lock time = 0: the transaction is propagated and executed at the instant of
creation.
- 0 < LockTime <= 500: the value is interpreted as a block height, ie the
transaction will be valid only after the block with height
equal to the lock time value has been published.
- Lock time> 500 million: the value is interpreted as a unix timestamp and
therefore the transaction will be valid only after the
date represented by the lock time value.
If you mean if the transaction has a timestamp, the answer is two:
Within the structure the transaction does not have a timestamp, but
rather a lock time.
The transaction could have an insertion moment in the block, which
depends on the block, because it is he who holds the timestamp as a
value.
A real use case:
My transaction has a block timestamp equal to 8/23/2019, 2:08:43 PM GMT + 2, this represents the time in which the miner started the cryptographic challenge, and it is the instant in which the miner has also taken into consideration my transaction including it in the block.
My transaction has a lockTime of 0 because it is an immediate execution transaction.
No one excuses that my transaction before the block was published was ALSO inside some other block with a slightly different timestamp
If you want have turn a detailed explanation of what and how a transaction works, I recommend this reading on bitcoin book
So transactions don't have a timestamp? – evannemo – 2019-08-23T12:45:39.900
No, the block has the timestamp and it defines when the miner starts the cryptographic challenge – vincenzopalazzo – 2019-08-23T12:46:53.063
I thought the cryptographic challenge happened before the block was added and once it is done, the block is actually added. – evannemo – 2019-08-23T12:47:58.400
The transactions are published in the block timestamp because all the data structure exists from the moment of publication and in the centuries to come :) – vincenzopalazzo – 2019-08-23T12:48:24.450
You got me confused. ( :P ) – evannemo – 2019-08-23T12:49:24.810
So a block can store a "future" transaction? that is mined but not actually calculated? – evannemo – 2019-08-23T12:50:59.677
The block stores a "future" transaction, because neither the block nor the transaction are actually verified and published, that is the work of the miner, who creates a block with the new transactions inside, solves the cryptographic challenge and publishes the block, I have added a real example to my answer – vincenzopalazzo – 2019-08-23T12:58:52.830
is this a kind of a state? the blockchain saves the locktime block after block and reduces it to 0 and then executes it? – evannemo – 2019-08-23T13:01:01.043
I don't understand, this "the blockchain saves the locktime block after block and reduces it to 0 and then " – vincenzopalazzo – 2019-08-23T13:10:41.757
I mean if the transaction is programmed to happen in 1/1/2030, will then every block include it until 1/1/2030? – evannemo – 2019-08-23T13:12:58.373
The lock time can be seen as a state, yes, the status of the transaction in my example is immediate, ie "as soon as possible". but do not confuse the timestamp with the locktime, the timestamp only indicates the age of the block, like a date of birth. – vincenzopalazzo – 2019-08-23T13:15:07.460
@evannemo No, the transaction will only be published in the first available block, but can only be spent after 1/1/2030 – vincenzopalazzo – 2019-08-23T13:16:30.543
All right! My question is, if two transactions are about to spent once they are published (locktime = 0), but Y is included on the current block and X on the next, even though X was broadcasted first to the network, doesn't this create problems? – evannemo – 2019-08-23T13:20:39.363
What problems are you talking about? before answering, I would like to have an example of a complete use case – vincenzopalazzo – 2019-08-23T13:35:25.700
For example, The transaction Y could be spent before X, even though X was broadcasted first. – evannemo – 2019-08-23T13:36:36.230
Absolutly yes, A transaction is not spent at the time of publication, but the newly published transaction spends a transaction already present on the blockchain called the comunemenete UTXO, I added an excellent reading to my answer, you will have answers to all your doubts – vincenzopalazzo – 2019-08-23T13:38:53.363