Avoided mixing dates and datetimes in the examples.

Refs #16023.

docs/ref/models/fields.txt

@@ -983,10 +983,10 @@ define the details of how the relation works.
     this with functions from the Python ``datetime`` module to limit choices of
     objects by date. For example::
 
-        limit_choices_to = {'pub_date__lte': datetime.now}
+        limit_choices_to = {'pub_date__lte': datetime.date.today}
 
     only allows the choice of related objects with a ``pub_date`` before the
-    current date/time to be chosen.
+    current date to be chosen.
 
     Instead of a dictionary this can also be a :class:`~django.db.models.Q`
     object for more :ref:`complex queries <complex-lookups-with-q>`. However,

docs/ref/models/instances.txt

@@ -135,7 +135,7 @@ access to more than a single field::
             raise ValidationError('Draft entries may not have a publication date.')
         # Set the pub_date for published items if it hasn't been set already.
         if self.status == 'published' and self.pub_date is None:
-            self.pub_date = datetime.datetime.now()
+            self.pub_date = datetime.date.today()
 
 Any :exc:`~django.core.exceptions.ValidationError` exceptions raised by
 ``Model.clean()`` will be stored in a special key error dictionary key,

docs/ref/models/querysets.txt

@@ -1945,6 +1945,17 @@ SQL equivalent::
 You can use ``range`` anywhere you can use ``BETWEEN`` in SQL — for dates,
 numbers and even characters.
 
+.. warning::
+
+    Filtering a ``DateTimeField`` with dates won't include items on the last
+    day, because the bounds are interpreted as "0am on the given date". If
+    ``pub_date`` was a ``DateTimeField``, the above expression would be turned
+    into this SQL::
+
+        SELECT ... WHERE pub_date BETWEEN '2005-01-01 00:00:00' and '2005-03-31 00:00:00';
+
+    Generally speaking, you can't mix dates and datetimes.
+
 .. fieldlookup:: year
 
 year
@@ -1958,7 +1969,7 @@ Example::
 
 SQL equivalent::
 
-    SELECT ... WHERE pub_date BETWEEN '2005-01-01' AND '2005-12-31 23:59:59.999999';
+    SELECT ... WHERE pub_date BETWEEN '2005-01-01' AND '2005-12-31';
 
 (The exact SQL syntax varies for each database engine.)