Its a good technique – but requires a huge amount of awareness of these semi-automatic behaviours – and if you have that awareness, you’re probably 90% of the way to addressing the issues. What would be fantastic is a layer of “effort” to get to these time-sucking apps. If its even just a few taps more to get into Facebook or Chat, it gives that other part of the brain a chance to kick-in and say “or I could…”. Perhaps something as simple as a much longer lock code on their phones, or a simple puzzle to solve.