Hello,

Yes, you can lock your choices if you are sure about it and is you don't want to make any changes in it.If you want to edit then do it before locking your choices.

Good luck.

You should lock seats whenever you feel you are okay with preferences. If you don't lock till deadline last preferences will be locked automatically so, even if you don't lock it won't matter. For surity of your choices you can lock on last day otherwise you won't know what was your last filled choices. After deadline you can't change anything.