Unfortunately it doesn't answer about what GUI do when you unlock the wallet.
I use the walletpassphrase to see if I still can remember my password and I don't want to transact, so im curious about what goes on when the GUI unlocks it when making a transaction.
If you need to do that, you can set a timeout of '1' second so your passphrase wont stay in your RAM for too long.
You also could use command
walletlock if you accidentally use default unlock duration and being extremely careful.