In short, you broadcast after the lock time.
Nice in short explanation.
So the following story will happen:Jack:" hey, lovely girl , I want to marry you and this is mine signed transaction, I will give you 1000btc one year later， you can verify it"
and Jackfucked Rose 364 days.
The 365th day Rose wake up and try to get those 1000btc but find the transaction invalid, Jack moved it to another address yesterday night. and..............Jack disappeared...............maybe saying same thing to Rose2..................
Story over. " promise is nothing , the nLocktime is a fucked idea in the design of bitcoin"
where are applause？
Instead of using nLocktime, you should create a P2SH address that uses OP_CHECKLOCKTIMEVERIFY. Done correctly, the Bitcoin sent to that address cannot be moved until after the locktime. This doesn't have the issues of the nLocktime transaction not being sent.