In the distant future, a brilliant, but timid theoretical physicist must accompany a team of reckless specialists and go back in time to prevent the last world war from ending to avert even greater atrocities.

"a brilliant, but timid theoretical physicist" = protagonist

must ... "accompany a team of reckless specialists" = response to inciting incident (possible antagonist?)

"go back in time to prevent the last world war from ending to avert even greater atrocities" = main character goal

Great main character, lots of potential for internal conflict, given the character will be afraid, but skilled in getting out of conflict. Implication is character arch of timid, moving through to courageous.
Missing link feels like it might be the inciting incident. What has motivated our timid scientist into working these reckless specialists? Guessing it might have something to do with the time machine ...

Orbital to a main character, are characters who either help or hinder. However, there is the idea of a contagonist, (think the Wizard, in the Wizard of Oz). Here they are not the principle villain (of course the Witch is the villain in Oz), and while the Wizard kind'a helps Dorothy, principally he hinders, by making it hard for her to find home. Basically, "reckless specialists" implies hinder, but he must "accompany" or work together, harmoniously and helpful in someway!

More to the point, who is the main bad guy? Perhaps it is a character related to starting the "last world war". A kind'a Ares villain character found in Wonder Woman, 2017.

I like it!

Possible Title: Give War a Chance