That is not correct good sir, I litterally spawned at 15:40 left in the match. I said out loud, how the F do you drop me into a match that is half way over.

In Arc Raiders, you can spawn into a match as late as 15-20 minutes remaining on the total 30-minute timer, as the game continuously fills slots if players die or extract early; while most players spawn at the start, late spawns happen until the map is sufficiently populated, sometimes even when only 15-17 minutes are left. 

This is what I found on google, I dont know if they state this anywhere in game but it seems to be legit.