Nice UI. I wish it would be possible to reorder the locations so that they can be offsetted correctly. Eg. for me Sydney is the first column. Then New York and I added Bangkok. Bangkok is closer to me timezone wise (i.e. they are a few hours behind) where as New York is nearly a day behind.
I'm in Sydney, and it's the first column in the UI by default for me. However I still can't add Auckland, Johannesburg, or any other Australian cities I've tried.
https://www.worldtimebuddy.com/