There’s been a little bit of vagueness about the details - even in the recent SFX article, Kurtzman hedged a little bit about just how much it overlaps with Discovery.

“The new show synchronizes with the first two years of Starfleet returning to its full form. The safest way to look at it is it’s like when Discovery ends, we begin - but there’s kind of a two-year overlap.”

So it might be (or parts of it might be) running concurrently with Discovery season 5. It probably doesn’t matter very much.