I just wanted to say, I remember seeing a much more morbid version of this idea somewhere o.o;
It was similar, with a timer that you were born with/could always see, but it was some sort of premonition that counted down the time until you'd die (via natural causes or something more sinister). I haven't seen that In Time movie, so I'm not sure how similar it is to this, but someone made a comment towards that idea saying something like:
"Imagine getting on a plane for vacation, and then as soon as it lifts off from the airport, the passengers, flight attendants, and the pilots all find that their timers become 30 minutes." Yikes.
I thought that was the direction you were going to go when I started reading the synopsis, but you put a pleasant spin on things at the end xD So I applaud you. Seems like a clever idea, regardless of the similarities to other things ;P
Have fun~