This app was mentioned in 4 comments, with an average of 3.25 upvotes
As a fellow ADHDer: This is going to suck, initially. There are all sorts of resources, but I've found that they just become either excuses when I have trouble with them or distractions when I am interested in them.
The best thing for consistent practice, for me, is to recognize that forcing myself won't work. That bargaining won't help. I have to step back and recognize that I use my mind all day and need it to be in good shape.
Bodhi Timer is distraction-free.
I'm using this app: https://play.google.com/store/apps/details?id=org.yuttadhammo.BodhiTimer
I wouldn't recommend just sitting until you feel its right, as it can lead to even more thoughts ("am I done yet? is this enough? can I get up?") than just waiting for the ding.
I'm using Bodhi Timer lately. It's very minimal; Exactly what I was looking for.
I'm a big fan of Bodhi Timer for Android.