Many companies have a clause that during notice period employee would not be entitled to any leave

2) these are then encashed during full and final settlement

3) if you avail leave for 12 days your notice period would get extended

1. Ordinarily, the provision of availing leaves does not exist during the notice period. The availed leaves cannot be deducted from the notice period.

2. Utilize the leaves during the full and final settlement.

Post resignation you may avail earned leave,

but you have to verify your company leave rules especially under the given situation.

It actually depends on your leave policy. If you go through the documents you signed while joining you will be clear whether your company allows employee to avail any vacation during their notice period. Anyhow the earned leave will be enchased in their full and final settlement.

Similarly, as some companies exhaust the employees complete Casual as well as sick leave on the day they submit their resignation, you may not be able to cash them up now.

Needless to say if the company takes only Earned leave into account and you avail leave during their notice period then it will not show any effect on the notice period.

Least but not the last, notice period is for smooth transition, you owe a lot of things to the company you departing and any abrupt leaving would hamper their workflow, so they may not allow you to adjust the leaves.

Anyways, you may negotiate with the HR for better outcome.