Holiday leave adjusted accordingly for part-time employees

Using the holiday leave function - when 28 days are used for a full-time employees holiday, can the system please automatically pro-rata this down for a part-time employee based on their working pattern? And can hours be used instead of days for this function? It would also be great if an employee changed working pattern, the holiday accrual is then automatically calculated again. An extra tab detailing an employees previous salary working pattern changes may help with this.