yes , blender will freeze as it will calculate texture size , and when you press ok then it will create list of data to download 
so overall it will freeze twice for few seconds , but after that it will come back to normal 

just move your mouse to that percentage, and in few seconds it will update automatically, 
moreover, if you want to check exact progress what addon has been downloading , then go to windows and toggle system console , 
it will give you all the information of download progress