I want to Add a new crawl component on SharePoint 2010? and want to know how much time it will take to complete the activity? also what all are the process SharePoint 2010 will do in this case?
I dont know how your farm and hardware looks like, but I only took seconds in my enviroment. However, I think that the index is gonna be recreated and re-distributed across the servers. Depending on your index size, it will take some time.
I recommend doing these operation during a maintance window.