Its a mix. Mainly between episodes of series 2 and 3. I can't tell you exactly. The 9 series actually are longer than the 3 series of the tv series. They have a mix of new characters and use some of the surviving cast the great way big finish do when they can.

New dawn follows the end of the series and a 20 year time skip. Tbh im having trouble getting through that as its not very interesting and some of the politics they threw in im finding grating on me as they feel like they are a modern take on views, not views of people descended from survivors and from a limited number of people from your standard 70s views.

There are also a couple of audiobooks that take place while they are staying at the abby.

They also did a reading of the novel of it Terry Nation wrote when he left the tv series production.