Just a little enhancement to the accepted answer given by Hiren above....
Presumably, you're not looking for the exact date and time (including the exact second!) that an item was published, so you're going to want to use second FieldOperator parameter (e.g. Criteria.GreaterThanOrEqual) when creating the ItemLastPublishedDateCriteria objects, so you can ...
I have seen this type of problem before. In our case the problem was due to schema changes.
When a schema metadata field data type has been changed you must
update all components using the schema
republish items using the schema
Check the metadata field type in the broker database to verify that all of the published metadata is the correct type.