With a PRO account, you are able to remove 100 friends per 24 hour period. 

And 500 friends in a 7 day period. 

But why?

Facebook limits the speed of activity on Facebook.

So you are only able to remove up to 100 at a time in a 24 hour period.

Facebook has updated their system for the speed of unfriending.

So we protect your account with putting this restriction for speed of unfriending

Hover with your mouse curser over the 100 limit and see when the countdown refreshes with 100 more friends.