I'll keep researching and see if I can come up with anything.
This is particularly difficult.
When instrumenting `org-add-planning-info` with edebug the
resulting timestamp always has its time portion (given and/or
end-time) ignored.
Tried it with both my personal setup and emacs -q. No luck.
I'm more likely to hack around this than figure out a proper
patch,
though I still consider it a bug that org-schedule is unable to be
informed by org-time-given and org-end-time-given I originally
described.
