I actually quite like the amount of dead space, as most time conversion tools I have used have been filled to the gills with information whereas I am typically only looking for one or two specific data points. To be honest, with many time conversion apps I often even struggle to distinguish a meaningful header, main content, and footer as they will often resemble some sort of industrial ticker. I know, different tools for different purposes, but that is exactly why I like this: it achieves simple comparisons simply.
I’m not saying add more things and information. I’m saying the opposite - remove things (white space) so I can look at more than three timezones changing (which is my use case as I run a ticketing site with venues around the world).