You know, I might call them and ask.. though most hatcheries try to include the same thing you ordered when they add free ones... I would certainly want to know.
Information I see says NO outdoor exposure for
3 weeks minimum after Marek's vaccine. Most accurate information I have seen in one place is...
https://www.backyardchickens.com/articles/the-great-big-giant-mareks-disease-faq.66077/
The ones I haven't brought in dirt for do enjoy bathing in the shavings well enough. It's kinda pricey and I don't do it... but another option MIGHT be some peat moss (garden department). Some people use it in their standard outdoor dirt baths.. to "help prevent" parasites, which shouldn't be an issue for you indoors.
Are you feeding non medicated starter? Since medicated counteracts the cocci vaccine?
Sounds like you are off to a good start... doing research before moving forward, it helps!