Heroes of the Lance can be completed in around 12 minutes.
Hydlide can be finished within a few hours with some RPG level grinding involved.
The first Dragon Warrior is relatively easy and has a battery save so you should be able to finish that one.
Defender of the Crown is a strategy game that can be completed in 10 minutes after you've practiced the basic gameplay.
Conflict, Desert Commander, Dino Riki and Dragon Spirit are some other NES games with short playing times.