well, you first have to set your nano to "time on wake". this allows the clock face to be the first screen you see when you power on or wake up your nano. to answer your question, you can't use it as a watch full time. once you power on or wake up your nano, the clock face will show for one minute only before going back to sleep. i would suspect the battery would die pretty fast otherwise. this is more of a novelty than anything else. but pretty cool nonetheless. so when you need to see the time, you simply press the button on the side. all the best.