I use Freshbooks (affiliate link) for all my contract and freelance work. A while ago I found ChronoMate (affiliate link), a Mac app for creating clients and projects, and tracking time spent on said projects. It’s great.
Part of ChronoMate’s secret sauce is its ability to notice when you’ve been idle or away from your Mac for a customizable amount of time. When you’re back, it immediately notifies you with a choice of what to do with that idle time.
After all, you may have actually gotten distracted by an iPhone game, so maybe you want to toss out that time. Or you could’ve been working with someone on a solution for your client, in which case you’d want to keep the time.
ChronoMate is great, and you can buy it for your Freshbooks account in two ways. You can subscribe to it for $1 per month in the Freshbooks add-on store, or you can buy it in the Mac App Store for a one-time payment of $20.
For what it’s worth: I subscribed to ChronoMate for two months to try it first, then bought it.