Ability to add a working pattern structure to each employee, linking in with the leave section.

We have a large number of staff that do not work a regular amount of hours each day. These staff do not work full-time hours but a chosen regular part-time week which they can split over chosen days and times during the week on a permanent basis. This means that all leave they book has to be done in hours (and the days equivalent is always showing wrong). Would it be possible to add a working pattern structure in the background so that leave can be booked in blocks and the system know the employees working pattern so can automatically work out the number of hours/days required ?