Equal sized timeseries for each id
generate_series() returns a SETOF dates between the first and second argument, at intervals specified by the third argument. Seems to be what you're looking for.

testdb=# create table customers(customer_id bigint);
CREATE TABLE
testdb=# insert into customers select 1;
INSERT 0 1
testdb=# insert into customers select 2;
INSERT 0 1
testdb=# select customer_id, d from customers, generate_series('2018-11-01'::timestamp, '2018-12-01', '1 week') AS d order by 1, 2;
 customer_id |          d          
-------------+---------------------
           1 | 2018-11-01 00:00:00
           1 | 2018-11-08 00:00:00
           1 | 2018-11-15 00:00:00
           1 | 2018-11-22 00:00:00
           1 | 2018-11-29 00:00:00
           2 | 2018-11-01 00:00:00
           2 | 2018-11-08 00:00:00
           2 | 2018-11-15 00:00:00
           2 | 2018-11-22 00:00:00
           2 | 2018-11-29 00:00:00
(10 rows)