Design of a database table

I'm trying to design a database table. First of all there are two
alternatives:
1-) Divide the table into two tables and make a join.
2-) Design a single table.

1rst alternative:
Create table data_periods(
id serial primary key not null,
period daterange,
project_id integer
)

create table data_periods_info(
id serial primary key not null,
data_periods_id integer,
data_sub_periods daterange,
stock1 integer,
stock2 integer,
CONSTRAINT data_periods_allotment_id_fkey FOREIGN KEY (data_periods_id)
REFERENCES data_periods (id) MATCH SIMPLE
ON UPDATE NO ACTION
ON DELETE NO ACTION
)

The table data_periods contains 1M rows and data_periods_info 5M rows.
I added an index to the table data_periods_info for the column
data_periods_id
I execute this query:
select
data_periods.id,
data_sub_periods,
project_id,
stock1,
stock2
from data_periods
inner join data_periods_info on data_periods_info.data_periods_id =
data_periods.id
where data_periods.period && '[2018-07-28, 2018-08-02]'::daterange
and data_sub_periods && '[2018-07-28, 2018-08-02]'::daterange

I got an execution time of : 1s 300ms

2nd alternative:
create table data_periods_second(
id serial primary key not null,
data_sub_periods daterange,
project_id integer,
stock1 integer,
stock2 integer)

I run this query;
select * from data_periods_second
where data_sub_periods && '[2018-07-28, 2018-08-02]'::daterange

I got such a execution time : 1s

Is it normal to get an execution time when using join relation greatest
than the execution time of a table contains million of rows and many
columns?