calendar-view-diary-initially-flag is a variable defined in `calendar.el'.
Its value is

Non-nil means display current date's diary entries on entry to calendar.
The diary is displayed in another window when the calendar is first displayed,
if the current date is visible. The number of days of diary entries displayed
is governed by the variable `diary-number-of-entries'. This variable can
be overridden by the value of `calendar-setup'.

You can customize this variable.