What I have discovered using regtest is that when the locktime is a block number an attempt to redeem will fail before that height is reached (i.e. it won't let you send a tx that has a future block number), however, when the locktime value is a unix timestamp then it will let you send the tx immediately (the tx just won't appear as confirmed).
Perhaps this is intentional - am mostly just reporting because it confused me (I had expected it to behave in the same manner as when the value is a block height).
