When the siblings ("Team Zero") arrive for Reginald's dinner invitation, there is an initial debate about who should do the talking. Vanya picks up a decorative conch shell and suggests that whoever is holding it should be allowed to speak - this is a reference to the 1954 novel "Lord of the Flies" (by British author William Golding), in which the castaway boys similarly decide to use a conch shell to indicate one's turn to speak to the larger group.
When The Handler talks to the Swedes, her Swedish is very poor. Later, when Five says "öga for öga," his pronunciation is much better.
When Reginald tells Five that he should attempt to time travel in shorter increments - "think seconds, not years" - it calls back to the Omega Device from Galaxy Quest (1999). The Omega Device would send the user back in time 13 seconds, "just enough time to redeem a single mistake."
Netflix went back to correct the credits of this episode from "Ellen Page" to "Elliot Page" retroactively in every episode of series 2 as a sign of proper integrity and respect.
Five comments he's older than Reginald when they're talking at the bar. Colm Feore, who plays Reginald, was born in August 1958, and would have been 5 years old in November of 1963.