This book (pre-1980s?) is about people who are exiled to the distant past for serious crimes. However, men and women are exiled to different time periods. So all men are sent to a certain time, but are separated from the women (who are sent to another period).
1 Answer
This sounds like Hawksbill Station by Robert Silverberg. It is a 1970 novel where political prisoners are sent to the pre-Cambrian period via a one-way time travel machine.
Hawksbill Station is a penal colony in the pre-Cambrian era created by the authoritarian United States government, using time travel as a means to exile rebels and political dissidents into the past. The colony houses only male exiles (a female settlement supposedly exists later in the Silurian era), who are sent there as a "humane" alternative to execution. The machine only works one way, so the prisoners are hopelessly marooned in the past.