org-agenda-search-headline-for-time

org-agenda-search-headline-for-time is a variable defined in `org-agenda.el'.
Its value is

t

Documentation:
Non-nil means search headline for a time-of-day.
If the headline contains a time-of-day in one format or another, it will
be used to sort the entry into the time sequence of items for a day.
Some people have time stamps in the headline that refer to the creation
time or so, and then this produces an unwanted side effect. If this is
the case for your, use this variable to turn off searching the headline
for a time.

You can customize this variable.