How to optimize sqlite datetime query for postgresSQL date?

Question

Python

Hello!
If everything is pretty clear in Sqlite, then Postgres has very laborious documentation.
Please help those who know how to make a similar function on posgresSQL:

There is a given function in sqlite used datetime. But unfortunately it doesn't work in postgre, because date has its own limitations, but is it possible to set them up in the same way? So that a certain point in time is counted from the current date

import psycopg2

    def get_records(self, user_id, within="all"):
        """Получаем историю о заказах"""
        if (within == "day"):
            self.cursor.execute("""SELECT * FROM orders WHERE user_id = %s AND order_date BETWEEN date('now', 'start of day') AND date('now', 'localtime') ORDER BY order_date""",
                (str(self.get_user_id(user_id)),))
        elif (within == "week"):
            self.cursor.execute("""SELECT * FROM orders WHERE user_id = %s AND order_date BETWEEN date('now', '-6 days') AND date('now', 'localtime') ORDER BY order_date""", (str(self.get_user_id(user_id)),))
        elif (within == "mounth"):
            self.cursor.execute("""SELECT * FROM orders WHERE user_id = %s AND order_date BETWEEN date('now', 'start of month') AND date('now', 'localtime') ORDER BY order_date""",(str(self.get_user_id(user_id)),))
        else:
            self.cursor.execute("""SELECT * FROM orders WHERE user_id = %s ORDER BY order_date""", (str(self.get_user_id(user_id)),))

Answer 1

Current time - now()
date_trunc() - date rounding

-- date('now', 'start of day')
date_trunc('day', now())

-- date('now', 'start of month')
date_trunc('month', now())

-- date('now', '-6 days')
now() - INTERVAL '6 days'

Answer 2

select current_date,
current_date - interval '6 day',
date_trunc('month', now()),
now();

Just a different set of features , choose the appropriate one.