setting 720min (12hrs) Appointments+

Hi Everyone and Happy New Year

When trying to put the work time setting to 720min (12hrs) Appointments+ will not give me the option to have proper start times like 5,6,7,8,9am and then have the 12hrs start, as i want my customers book me for a full day of photography

has someone had this problem and solved it could you please let me know how

Thanks in Advance