Unfortunately it doesn't have error handling, so when you do += 8 hours and it fails, it won't return a Go error, it won't throw a Go exception, it just silently does the wrong thing (clamp the duration) and hope you don't notice...
It's simplistic and that's nice for small tools or scripts, but at scale it becomes really brittle since none of the edge cases are handled
I thankfully found out when writing unit tests instead of in production. In Go time.Time has a much higher range than time.Duration, so it's very easy to have an overflow when you take a time difference. But there's also no error returned in general when manipulating time.Duration, you have to remember to check carefully around each operation to know if it risks going out of range.
Internally time.Duration is a single 64bit count, while time.Time is two more complicated 64bit fields plus a location
It's simplistic and that's nice for small tools or scripts, but at scale it becomes really brittle since none of the edge cases are handled