Hi, Rick,
I don't know specifically how to determine the date/time a particular table was last updated - I'm sure Sergey or someone else might have an answer.
Having said that, one thing you might consider is some type of DateTimeLastUpdated column on your tables. You could implement an insert/update trigger that automatically updates the LastUpdated column anytime an insert/update occurs.
You could then perform a SQL MAX() on the column to determine the datetime last updated...and additionally, you'd also be able to tell the last time any particular row was added/updated.
Hope that helps...
Kevin