According to web guru Jakob Nielsen, for any website, the first 10 seconds of a visitor on it is the most crucial. And if by chance the website manages to engage him for more than 10 secs.
The next level is the 20 second stay, which if any visitor passes, he is bound to make a sale or atleast become a recurring visitor that might at some point of time translate into a sale.
It is very important that for a website to hold a visitor long enough to stay it has to make sure to have a headline that is not just catchy but also powerful in a sense that it not just the first 10 second on your website but the first 3 second range is also very crucial which is decided by your headline; a to enter or not to enter scenario.