J'ouvert, or "Dirty Mas", takes place before dawn on the Monday (known as Carnival Monday) before Ash Wednesday. It means ""opening of the day". Revelers dress in costumes embodying puns on current affairs, especially political and social events. "Clean Mud" (clay mud), oil paint and body paint are familiar during J'ouvert. A common character is "Jab-jabs" (devils, blue, black or red) complete with pitchfork, pointed horns and tails. A King and Queen of J'ouvert are chosen, based on their witty political/social messages.

When does  Dirty Mas take place on the Monday before Ash Wednesday?