Four O’clock
اَلسَّاعَةُ الرَّابِعَة

Five O’clock
اَلسَّاعَةُ الْخَامِسَة

Six O’clock
اَلسَّاعَةُ السَّادِسَة

Seven O’clock
اَلسَّاعَةُ السَّابِعَة

Eight O’clock
اَلسَّاعَةُ الثَّامِنَة

Nine O’clock
اَلسَّاعَةُ التَّاسِعَة

Ten O’clock
اَلسَّاعَةُ الْعَاشِرَة

Eleven O’clock
اَلسَّاعَةُ الْحَادِيَةَ عَشْرَة

Twelve O’clock
اَلسَّاعَةُ الثَّانِيَةَ عَشْرَة

Note :
You need to use the definite prefix article "ال" with the ordinals because you’re referring to a specific hour and not just any hour.