"Day" from 8am to 3am

Hi folks,

I have a special application that considers a playday to be from 8am to
3pm the next morning. The system then does maintenance from 3am till 8am
(if necessary).

I'd like to ease application development by creating a new kind of
"playDay" to query from. For example:

SELECT * FROM table WHERE timestamp IN date_trunc('playDay', timestamp);

Any ideas?

Where should I begin? Or is this all just wrongheaded and should I put it
on the application level?

-judd