Jocko Willink posts a picture of his watch during his workout every morning, usually in the 4:20 to 4:30 range.
Would you post what time you worked out everyday? Would you post how many hours you worked today? Would you post how many calories you ate today? There is a reason why this isn't a common way for people to use the internet.
I can see someone doing this and posting it online to keep themselves accountable.