The law permits an employee to request his employer a reduced work schedule, so that he/she can take care of a minor. Maximum age for the minor(s) under care of the employee is 12 years, for the request to be granted.
Unless the Convenio in place for your line of work permits entire workdays to be eliminated from the work schedule, you can only skip hours on a daily basis, between 12,5 and 50%.
You need to give 15 days notice and need to indicate first and last day of the proposed reduced schedule. It´s up to the employee to propose a schedule that best fits her/his needs, but the Convenio in place might state additional conditions, so pertinent to check that, before making the application with your employer.
Note* You can NOT be fired for requesting a reduced work schedule.