How to Add Time-Budget and Time-Spent to Story?

How can I attach a budgeted time (in 1/10 or, 1/4 hr increments) to my stories and then enter an actual-time number when finished? This would be monumentally helpful to us as the client as we have a limited number of hours available to us for the remainder of our project (i.e. 350 hours) and need to 'spend' every one very carefully.