i live my life in 2 hour blocks run at home by my computers freeware app egg timer i got at
for everything sorter i use mutable of the same app. when time is done it pops into the foreground and playing a wav file forcing you to deal with it before continuing (i use a stargate klaxons ring-tone (switching between SG-1and Atlantis) downloaded at:
i came to the 2 hours block by experimenting by having a friend come in and beak my focus at different intervals and then comparing notes on how i reacted with the interruption. the notes were focus amount, announce, and time back to focus.
i use a klaxon for the reason that the military spent years developing a annoying non-avoidable sound to use for all alerts get a AUTHENTIC NAVY ALARM SOUND go to:REPORT ABUSE