President Yahya Jammeh has enforced the change, in effect from today (February 1), which applies to everyone who works in the public sector.
The hours lost are made up in the other weekdays, as workers will now be expected to turn up from 8am to 6pm, Mondays to Thursdays.
The change is primarily aimed at the Muslim community, as Friday is the day of prayer for their religion.
A statement read: "This new arrangement will allow Gambians to devote more time to prayers, social activities and agriculture - going back to the land and grow what we eat and eat what we grow for a healthy and wealthy nation."
However, the move has been met with skepticism, reports BBC News.
Some have claimed that it will be disruptive as the private sector will still be working on Fridays, while others have expressed concerns that the country will become lazier as a consequence.