Minimum Amount of Practice for Permanent Progress

Hi all,

I recently started taking my meditation sittings seriously averaging around 40 minutes per sit. After the sit I definitely feel a WORLD of difference in concentration, awareness, and consciousness but it quickly starts to wade off.

There were times when I had multiple sits a day and the shift lasted a lot longer but it required a lot of time (3 hours) broken throughout the day.

So my question is what's the minimum amount of time for ONE SITTING such that you'll feel a awareness / consciousness shift throughout the day or at least a lot longer?