Where it's done if needed, specifically? In Electrum or something along the lines of it?
You can do nLockTime in any known wallets, Bitcoin Core and Electrum will support it. However, it doesn't exactly lock the coins, they're only meant to ensure that a transaction cannot be confirmed before a certain time or a certain block height; not a foolproof way to ensure that users cannot access their funds.
OP_CSV, on the otherhand guarantees that you cannot spend the inputs until its expiry. I'm not aware of any elegant GUI implemented with it, perhaps others can chime in.