Dr. Stein says "until someone gives machine guns to the Confederate Army." In Harry Turtledoves "Guns of the South," a group from South Africa sends AK-47's to the Civil War, which changes the outcome of the war in the CSA's favor.
This episode's title is an homage to the licence plate ("Outatime") from the Delorean in the Back to the Future movies. Both this series and those movies deal with time travel and the consequence of even the most minor change.
Christiaan Westerveld (King Louis XIII) has previously appeared in another 'Arrovwverse' TV show but as another, unrelated character. He appeared in an episode of 'The Flash' as a mugger.
Michael Germant (German Sailor) has previously appeared in another 'Arrovwverse' TV show but as another, unrelated character. He appeared in an episode of 'Arrow' as the bartender.
When Einstein regains consciousness, Dr Martin says to him "Guten morgen". That is "Good morning" in German.