OK so here's what I did...I created a view in my database where there is a record for each office, and fields for the current date, current day of the week, and current time.
Then in my MXD, I joined my office locations layer to this view by Office ID, and in my query, I included in my definition query the following: CurrDayOfWeek <> 'Saturday' and CurrDayOfWeek <> 'Sunday'
The view definition was:
SELECT OFFICE_NO, CURRENT_DATE AS CurrDate, TO_CHAR(sysdate, 'DAY') AS CurrDayOfWeek, ((TO_CHAR(CURRENT_TIMESTAMP,'HH12:MI AM'))) AS CurrTime
FROM SDE.FEATCLASSNAME