Schools Admission Time and reputable schools (Riyadh)

Dear All
This is my first post as i am moving soon to Riyadh. I urgently want to know if there is specific time to apply for schools for next year starts September Protected content my two young sons Grade 7 and grade Protected content and 8 years).
Also if there is good reputable schools for International and/or IGCSE .

Thank you
Hussein Aboelnaga