Contracted hours changes should work before effective date of change

I have a payroll set up like a school, where pay spines are used. Salary can only be amended in the employee's record, not on the payslip, however contracted hours can't be changed until the day of or after the effective from date. This won't work where there are new starters beginning late in the month, or contract changes where basic pay needs amending - we won't always be able to wait until the specific date of change, we need to be able to change this no matter what the date is.