Not to shoot down your aspirations but there's actually quite a good one already on the market.https://play.google.com/store/apps/details?id=com.nwalex.meditation&feature=search_result
You might try downloading that one and seeing how you can improve upon it's design.
One thing that might be helpful that that one doesn't offer, is the ability to set "softer" and "harder" bell strikes, (perhaps three different "hardness" settings?) more in line with Zen practice, as well as perhaps offering a the option to let a final strike "trail off" in a more natural way rather than abruptly end the sound.
Also, I think some diversity options in the gong and bell types would be appreciated by many.
Perhaps not only a few varieties of "Zen" gongs, but also bells, and wooden blocks and clappers as well as some Tibetan sounds.
There is also a "zen alarm clock" made by Now & Zen that uses a chime that rings down in a Fibonacci/Golden ratio spiral of strikes.
Not everyone would use that option, but I'm sure some yoga people and others would be thrilled by the option.
Good luck on you programing, it's nice to see more Buddhist apps in the Marketplace.
"Life is full of suffering. AND Life is full of the Eternal
IT IS OUR CHOICE
We can stand in our shadow, and wallow in the darkness,
We can turn around.
It is OUR choice." -Rev. Basil Singer
" ...out of fear, even the good harm one another. " -Rev. Dazui MacPhillamy