Longing Heart (2018)

The two travel to meet an old love............................................................................................................................

As our main plot is time traveling, both dramas are about this. It's different in many things. This is about a man who time travel to propose his first love and to stop her from getting married.

Let's not forget the original Japanese drama starring Tomohisa Yamashita.
Time travel - romance - comedy

both male protagonists manage to go back in time to win their first love----------------------------------------

both are done by the same screenwriter, and both are scifi fantasies. one is about time traveling and the other is about dual universes ;D

Both involve the lead meeting a younger version of themself
Both involve some kind of time travel
(Something something 100 letters)

Both dramas have same feel.
Both dramas are about MC trying to save his first love from death
Both involve time travelling

Parallel love is about a woman going back in time and meeting her younger self, and trying to help her cope with a break up that happened to her. She meets her ex-boyfriend again, but knows he is bad for her this time.

A male lead who can't confess to his first love. He travels back in time and returns to his high school years. This time he tries to help the girl he loves to confess to her past self..................................................

-Time travel
-Regrets
-Both the Dramas
-School drama
-First love
-Separation
Longing heart the ml travels back to time as his adult self there he met his younger self and tried to help him win his first love heart

Borh dramas deal with time travel and the attempts of the main lead to change the past/future. The decisions of the main lead are of great importance for the time-related plot and how small changes alter a person's course in life.

Longing Heart and Reunited worlds are similar in certain points like how they are both time themed drama. Both without much focus on the details on how time was bent
—The school setting is important for the plot
—precious familial ties and moments. The main leads understand how their actions or absence affected their surroundings
—high school first loves

This is the Chinese version of operation proposal. The only thing that is common is time traveling. Heart melting romance in both dramas are same

both the protagonists of the drama manage to go back in time and give love advice to their teenagers themselves

both protagonists of the drama manage to go back in time and give love advice to their young selves.