Firms are free to set their own start and end times.
Earlier this month, the UAE government announced the Ramadan working times for public sector employees will be from 9am to 2.30pm, from Monday to Thursday, and from 9am to 12pm, on Fridays of every week.
Schools in general are given flexibility to manage their own day, but there are different rules in each emirate.
Last year the KHDA notified Dubai schools they could open for a maximum of five hours, but they could choose their start times in consultation with parents.
In Sharjah schools were allowed to open for "between 3 and 5 hours".
Given that schools in the emirate now operate a four day week, the reduction in school operating hours is likely to be less generous.
Ramadan is expected to begin on April 2nd. The actual start date is, however, confirmed by the UAE’s moon-sighting committee.