This. TagTime (which is Free, made by the Beeminder people, and plays nicely with their goal tracking product if you want it) is scheduled such that you are equ

This. TagTime (which is Free, made by the Beeminder people, and plays nicely with their goal tracking product if you want it) is scheduled such that you are equally likely to be 'pinged' at any moment as any other, with an expected value of every 45 minutes. I have been using it for the past five years or so. Apart from being a gloriously hacky bundle of perl scripts (and not playing wonderfully well when run on multiple machines) I've found it perfect. There's also an Android version nowadays I think, though. That blog link explains it well.