Hello,
IMHO it needs a 3nd date-mode. I use deadline for all thinks
that have to be done until the deadline-date. I use scheduled
for a fix date ...
and what about thinks that could start at a date "or later".
I tried to fix it by using a time for fix and no time for
non-fixed or has-to-be-start dates, but this is no solution,
because there are todos that have to be done on a fix-time and
others only on a fix day.
But never the less I use a lot of planning tools but org-mode
fits best for all my needs -
thanks - Michael