Hah. @jolmg & I almost collided to the second. :-) That stackexchange link had an answer with the INC_APPEND_HISTORY_TIME setopt which seems to work without SHARE_HISTORY (I think using his whole stackexchange answer might still result in 0s..at least it did for me when I ran it in a precmd() instead of adding the hook, but it could always be something else varying between his & my setopts).