How does this compare to, say, Pomodoro? That's been very effective for me: each morning I configure a list of things to do, then work through it in order with defined times for breaks, checking my email, etc.
1. You don't have to stop when the timer is up. The timer is really a forcing function to get you into the zone. When you're being productive, keep going!
2. You can adapt it to longer intervals if that better fits your day and schedule - plan for 50min work and 10min breaks?