You can set the locktime to the blockheight you want the transaction to be included on the block.
the locktime field is interpreted in two ways: as a block height and a date-time.
in other words you can also set it to a datetime. all you have to do in order to do that is to convert your datetime object to epoch:
for example Saturday, February 29, 2020 4:19:08 AM is 1582949948 then use that integer in your locktime field in little-endian order.