Keep
an audit-record of how each interval of 40 minutes (inclusive of five-minutes-breaks)
actually gets used throughout the day.
The
five-minutes-breaks can be utilized for doing anything that refreshes you.
The
audit-record will give you a pretty good idea of how your alertness levels
change during the day.
Use
the periods when your concentration is at peak for the important tasks and
the ones with low alertness levels for repetitive tasks viz: filing, photocopying…