Once you have unlocked Special Ops for a region and you enter the Special Ops menu you will see a timer near the top of the screen, below your "LVL". This 24 hour timer shows the amount of time you have to complete a mission. The timer begins when a new day begins according to our servers and resets after it has counted down to zero. When the timer resets you will be able to attempt a new region if there is still time in the week.   

If you have entered a Special Op and actually played a mission, when the timer reaches zero you will not be able to replay that Special Op until the week has ended. The week is defined by the day countdown located below the list of regions, at the top of the weekly leaderboard. 

Any rewards earned in a week will be credited shortly after that week ends and a new week will begin, allowing you to replay all Special Ops mission you have unlocked.

In order to attempt a Special Ops mission you need to equip weapons that are at or below the region level for that mission. So in order to play a region 4 Special Op you would need to equip weapons that are region 4 or below.

Bonus skill coins can be earned through killing enemies with head shots, killing multiple enemies in a single shot, completing a mission quickly, or being accurate with your shots.