Timezones are annoying, and alas I often found myself needing to do timezone time translation across multiple locations simultaneously, so I built https://timezon.es (in jQuery - it was a while ago). An early version had ads, but with total earnings of ~$2 after multiple months of operation I never bothered re-adding them after a redesign :)

I guess doing any advertising at all might generate traffic, but it seems unlikely ad revenue would cover ad spend. For now I just appreciate its being there 'cause I find it useful :)