date -jr takes a unix timestamp (number of seconds since midnight jan 1 1970 GMT) and converts it to the equivalent local time. I'm betting you're running in a timezone that is one hour ahead of GMT. Ten seconds after midnight jan 1 1970 in GMT is one hour and ten seconds after midnight jan 1 1970 in CET, for example.
If you use the "-u" switch, you'll get UTC time. So this might work for you:
date -jur 10 '+%H:%M:%S'