Hello, can i remove time from date/time question????? i want only date..thank's

Do you mean at the results table?

yes..now i have 2015-09-18 00:00:00 but i want only 2015-09-18..can i?

No, because the field type at the database is set to include the time.

Only alternative solution would be adding a hidden equation question and storing the cut off date there. Use this equation assuming the date question uses code "date":
{substr(date,0,10)}

sorry, but where i have to add this string?

Create a question of type equation and add this directly at the question text. Adjust the question code as needed.