Casual discussion amongst spiritual friends.
I use an iPhone and use the app "Samsara." I rather like it. You can set how long you'd like the mediation to be, with bells at certain intervals. Also, you can turn off the countdown if you find that distracting, and are left with a white circle that slowly fills in orange till your mediation is over. It's a very nice, bare bones timer, that I've experienced no issues with.
Insight Timer is released open source, and use Lotus Bud on my iPhone and with Do Not Disturb. I'm also checking out Mobile Price in Australia it works great.