[This discusses events in older Star Wars movies without spoiler space. Spoiler space is used for The Rise of Skywalker spoilers.]

###When was Rey born?

From Wookiepedia, I'm piecing this together:

Star Wars: The Force Awakens: The Visual Dictionary states that Rey is nineteen years old during the events of Star Wars: Episode VII The Force Awakens, which is dated to 34 ABY by Star Wars: Galactic Atlas. Therefore it can be deduced that Rey was born in 15 ABY = 19 BSI.
_{15 ABY}

Using Wookiepedia's terminology, 15 ABY = 19 BSI = 19 years before the Starkiller Incident, i.e., 13 years before e.g. the Starkiller base was destroyed.

###Let's subtract say 30 years, to estimate when her parents were born.

Thus it's probably a reasonable guess that Rey's parents were born somewhere around 50 BSI. It likely Rey and her parents and grandparents are all humans. Wookiepedia has a useful timetable which lists:

53 BSI: End of the Clone Wars and transformation of the Republic into the Galactic Empire. Anakin Skywalker becomes Darth Vader.

This is probably in the ballpark (maybe +/- 15 years) of when...

...Rey's father was born. So pre-resurrection Darth Sidious had a son, Rey's father.

So it probably happened somewhere during the prequel trilogy.

[This discusses events in older Star Wars movies without spoiler space. Spoiler space is used for The Rise of Skywalker spoilers.]

When was Rey born?

From Wookiepedia, I'm piecing this together:

Star Wars: The Force Awakens: The Visual Dictionary states that Rey is nineteen years old during the events of Star Wars: Episode VII The Force Awakens, which is dated to 34 ABY by Star Wars: Galactic Atlas. Therefore it can be deduced that Rey was born in 15 ABY = 19 BSI.
_{15 ABY}

Using Wookiepedia's terminology, 15 ABY = 19 BSI = 19 years before the Starkiller Incident, i.e., 13 years before e.g. the Starkiller base was destroyed.

Let's subtract say 30 years, to estimate when her parents were born.

Thus it's probably a reasonable guess that Rey's parents were born somewhere around 50 BSI. It likely Rey and her parents and grandparents are all humans. Wookiepedia has a useful timetable which lists:

53 BSI: End of the Clone Wars and transformation of the Republic into the Galactic Empire. Anakin Skywalker becomes Darth Vader.

This is probably in the ballpark (maybe +/- 15 years) of when...

...Rey's father was born. So pre-resurrection Darth Sidious had a son, Rey's father.

So it probably happened somewhere during the prequel trilogy.