Episode 3x18 - "Carentan" is included as the time dilation bubble was caused by Adam who was somewhere below the area in Hollow Earth near a fissure which allowed the rogue bubble to escape up to the surface.
This is a special grouping of episodes that involve both Adam Worth and Hollow Earth. These episodes are directly related from one to the next, literally starting back-to-back of each other as they occur across the span of several days in-universe.
While Episode 3x02 - "Firewall" and Episode 3x06 - "Animus" both include information that set-up these episodes as seen in Episode 3x07 - "Breach", they do not chronologically occur immediately in-universe before this block, thus they are excluded.
These two episodes occur very closely chronologically wise in-universe. Adam Worth intentionally sets his time machine off to destroy Praxis. When this happens, Praxis' containment fences fail, letting loose giant Psych Worms. It is unknown how long it took for the worm to surface, but it is known that Helen and Will spent 3 days, 8 hours, and 26 minutes in Virgil's treatment. Once back at the Old City Sanctuary, an unknown amount of time passes until Hollow Earth Refugees start to surface. Their primary reason to surface was due to lack of their water supply which had stopped when Praxis was destroyed. Based on dwindling resources and biology, it's estimated that humanoid organisms can only last up to about 5-7 days without sufficient water intake (this is the maximum stretch possible as the usual time frame is about 3 days on average with zero water consumption). Considering already known time to have passed, Episode 3x20 - "Into The Black" starts potentially the very next day or two after the end of Episode 3x19 - "Out of The Blue".
This is the Season 3 cliffhanger finale that was continued into the beginning of Season 4. These episodes are specifically relating to the event of several hundreds of Hollow Earth Abnormals invading the surface.
These episodes involve Dr. Will Zimmerman's mother, Mary Anne Zimmerman. Since her tragic death by an Abnormal lizard creature in 1985 when Will was just an 8 year old boy, it has left a profound psychological impact on him that he's carried around with him throughout the rest of life.
Episode 1x10 - "Warriors" is included due to Will admitting to Magnus that he used to daydream about his mother every chance he got.
Episode 4x03 - "Untouchable" is included due to Greg Addison accusing Will of using Magnus as a replacement mother.
Episode 4x08 - "Fugue" is included as Will reveals he doesn't like to sing as that's what his mother used to do.
This is a small cluster of episodes that occur chronologically very close to one another, possibly over the course of a single week in-universe based on the apparent ongoing friction between characters. These episodes deal with Dr. Helen Magnus and her relationship issues with both her biological daughter Ashley Magnus and her adopted son Henry Foss. While Episode 1x02 - "Sanctuary For All, Part II" sets up Episode 1x07 - "The Five", it does not occur immediately before, thus is not included.
It is unknown for how long Ashley and Helen had stayed in Rome after the end of Episode 1x07 - "The Five". What is known is that Ashley gives Helen a silent treatment starting during their recent flight home and has continued to do so since then as she's mentally dealing with the personal revelation that John Druitt is her father and the betrayal she feels towards her mother for not being the one to tell her, something Helen wants to talk about in Episode 1x08 - "Edward". Another persisting issue from "The Five" that carries over into "Edward" is Henry and his struggling to control his body's HAP metamorphosis; something that is deeply disturbing to him that he wished Helen was there for, which also happens to be something that Helen regrets missing while she was in Rome. Based on these two factors between Ashley and Henry, it seems an estimated day or two had passed between the end of "The Five" and the start of "Edward" as emotions are still very raw/fresh and currently ongoing between mother and children.
It is unknown how much time had passed between the end of Episode 1x08 - "Edward" and the start of Episode 1x09 - "Requiem", but what is known is that "Edward" itself occurred over the course of about 48 hours (2 days) as that was the amount of time Will was given from Det. Joe Kavanaugh to investigate the Glen Meyers suicide case. In "Requiem", Will had noticed Ashley's recent silent behavior, to which Helen references the "talk" they just had in "Edward" and how frustrated she is at not being able to relate to her daughter. Based on this evidence, with how relevant the fallout from "The Five" continues to be, not much time seems to have passed from the end "Edward" to the beginning of "Requiem", maybe starting the next day or so afterward.
Considering all of the factors across the three episodes, from the start of Episode 1x07 - "The Five" to the end of Episode 1x09 - "Requiem", chronologically in-universe it seems that at most maybe a week total had passed.
"Revelations" is the Season 1 finale cliffhanger arc that concludes as the Season 2 opener arc "End of Nights", which follows-up in Episode 2x03 - "Eulogy".
Episode 1x10 - "Warriors" is included because of Gregory Magnus' knowledge of the Source Blood, plus his deadly fighters were to be used in the 'Abnormal cleanse'. 'Charlie' was a mole used to report back to the Cabal, making sure the "asset" was in place for this arc.
These episode deal with the temporary resurrection of the Vampire species that periodically occurs from time to time throughout the series. This group consists of episodes revolving around Nikola Tesla's personal experimentation as well as including a legitimate awakening of a Queen vampire from stasis who had plans to revive her species.