Perfect!
I found myself often scrolling through social media and news pages while I was supposed to get work done. They call it procrastinating. This simple yet effective add-on blocks chosen URLs after my set time limit and remind me to focus on my work. Of course there are some workarounds for the block, but this is a solid treshold for work avoiding behaviour.

Its really workin! Thank u!
Guys, use this way for writin sites 4ex - *://*.vk.com/*

Does exactly what it says. Straightforward configuration (from the Add-ons Manager in the menu)