Added a new time difference calculator

https://www.onlinecalculators.app/time-duration-calculator

I researched keywords to find the demand around this calculator and saw not a lot of competition is out here. If there is, I know I can make it better. So launched this calculator as a new addition this weekend.

I recently applied for Google AdSense since I was getting okayish traffic. But Google rejected my application. They said I need more content on the website. But this is not a content website. It is a utility web app. Well! fcuk google ad sense. I will find a different way to monetize.