anti-RSI feature in screen? like xwrits

[Miernik]

I'd like to have a feature to have screen block itself for 5 minutes
every hour, to prevent Repetitive strain injury.
http://en.wikipedia.org/wiki/RSI

xwrits is a program which does such a thing in X.

I'd like to implement it inside screen.
It's a bit like a reverse-screensaver (blocks the screen not if you
don't type anything for a specified period of time, but when you type
for a specified period of time without a break.

If such feature is not available, what't would be the simplest way to
code it? I'd try to code the feature myself, but I'd be grateful for
some hints.

-- 
Miernik