Storing seconds, retrieving sensible data

I want to construct a time period, i.e. say a user has 1 month, 3 days
and 10 hours to do something. I want to store this information in a
database, and instead of storing this information in 3 fields, I want
to store it in one.
I have 3 select boxes, one for Month, Days, and Hours, and I'm using
"before_save" to convert the selected value into seconds.

However, when I retrieve the information from the database what would
be the best way to retrieve the Month, Days and Hours information
again?

Thanks in advance.