FND PLSQL "DECLARE
    l_to_date DATE := fnd_date.displaydate_to_date(:!VALUE); -- Date in 'To Date' parameter.
    l_from_date DATE := fnd_date.canonical_to_date(':$FLEX$.FND_STANDARD_DATE'); -- Date in 'From Date' parameter.
BEGIN
    IF l_to_date IS NOT NULL 
        AND l_from_date IS NOT NULL 
        AND NOT l_to_date BETWEEN l_from_date AND l_from_date + 30 THEN
        FND_MESSAGE.SET_NAME('FND','Select Value with in 30days'); 
-- Better to seed one message name instead of hard coding the text.
        FND_MESSAGE.RAISE_ERROR;
    END IF;
END;"