[neotokio]

Optimal time for breaks vary. You should figure it out yourself. When it comes to productivity it's 52 minutes work time vs 17 minutes break[1]. There is also 'pomodoro technique'[2]. There is also kind of interesting work (which can be extended to topic of procrastination) done by Mihaly Csikszentmihalyi [3], namely - idea of 'Flow'.

From personal perspective I would say to also look at how do you eat, sleep, spend your free time and take any substances (alcohol, drugs, cigarettes...). Even if this is not an ongoing thing but occasional it has tremendous effect on ability to concentrate for long periods of time. Excessive carbon based (or worse, sugar based) diet can make you hyperactive (same as excessive fat based diet can make you dull btw). Again, that's a personal perspective.

As last resort, there are some supplements which could help you with concentration, not pharmaceuticals, there are a lot of natural nootropics[4] you can get anywhere.

Bottom line, if you waste time on Internet - just stop. There is no other way. Blocking websites can help, but in the end, you need to choose not to visit those. It's addiction as any other. And don't treat this post as advice, everybody needs to figure it out himself.

[1]https://lifehacker.com/52-minute-work-17-minute-break-is-the... [2]https://en.wikipedia.org/wiki/Pomodoro_Technique [3]https://en.wikipedia.org/wiki/Mihaly_Csikszentmihalyi [4]https://en.wikipedia.org/wiki/Nootropic#Herbs