When is it obligatory for girls to be circumcised, and at what age?

All praise is due to Allah, and peace and blessings be upon the Messenger of Allah, and upon his family and companions. To proceed:

There is no specific time for the circumcision of boys and girls. However, it is preferable for it to occur before the time when it becomes forbidden to look at the 'awrah (private parts). Some scholars recommend it before the seventh day of birth. The circumcision of girls is permissible or a commendable act, not an obligation. There is no established prohibition or specific time for it, and the default ruling in such matters is permissibility unless there is evidence to the contrary. Allah knows best.