Ripper, by Stefan Petrucha

Orphan Carver Young has some general fantasies about becoming a detective, and devours novels and stories about  great sleuths, as well as serialized and sensationalized mysteries.  When ex-Pinkerton Detective Albert Hawking, cranky, contentious, eccentric, brilliant, and crippled, offers to take Carver on as an apprentice to share all he knows, Carver is ecstatic, even though it means living (for a reason I never really understood) in a private floor at the top of a mental institution, and getting more questions, half-hints, and criticism from Hawking than direct answers.  Carver's first and main "case" is to figure out the identity and possibly location of his father based on a scrap of a letter sent to the orphanage many years before.  As part of this Hawking introduces him to the "New Pinkertons", an underground (literally) and top-secret detective agency endowed by Alan Pinkerton upon his death. Hawking was head of the agency until his injuries forced him to give the reins to another former Pinkerton agent, Tudd, who is devoted to "gadgets" and buys many, many new mechanical, electrical inventions to help the secret agents with their investigations, and who is obsessed with catching a murderer, convinced it is the return of Jack the Ripper.

Tempest by Julie Cross

19-year-old Jackson Meyer can time travel.  Not much, usually just back a few hours or days.  And when he does go back, nothing he does actually impacts the future - no one remembers interacting with him if it happened on one of his jumps, if he hurts himself he isn't seriously damaged when he gets back, and if he does something on one of his jumps, like break a window, that thing is undone when he gets back to the present.  It's not really serving a purpose, but he's having fun experimenting, and keeping it a secret from everyone but his science genius friend who is helping him figure out why it's happening and how to use it.  At least it is all fun until some people who also appear to be able to "jump" back in time show up at his girlfriend's college dor, attempt to kidnap Jackson, and kill his girlfriend in the struggle.  Now Jackson has jumped back 2 years, farther than he's jumped before, and no matter how hard he tries, he can't get back to his "real" time.  And the Enemies of Time are still after him.

Ruby Red by Kerstin Gier

1st in Ruby Red series.  Sequel is Sapphire Blue.  First published in Germany.

Gwen is 16 and lives with her mum, siblings, grandmother, aunt and cousin in an upperclass London neighborhood.  Her extended family doesn't pay much attention to her, focused on her cousin, believed to be the carrier of the time-travel gene that runs through her family and sure to show up very soon in the form of an abrupt trip to somewhere in the past.  But all is not as it seems.  Since a mathematical formula had worked out that Gwen's real birth  date was the birth date of the next time traveler, and her cousin was also born that day, Gwen's mum and (late) father secretly falsified her records to indicate Gwen was born the day before, allegedly in the hopes that she would be able to live a normal life (and since she was born at home with a midwife, no one was the wiser.

The Book of Blood and Shadow by Robin Wasserman

Nora has a pretty good life - yes, her brother is still dead and her parents are still withdrawn into their own self-absorbed worlds, but she has made a new family of sorts, with bright, charming, boy-wonder Chris and his lovely, capricious girlfriend Adriane as her best friends, and moody, quiet, scholarly Max as her boyfriend.  She also has an engrossing translation project for a local professor to strengthen her link with Chris and Max - while they work on translating the "important" parts of an ancient mystical document the professor is obsessed with, Nora translates late 16th century letters from a young woman, stepdaughter to a great magician - busy work to the professor, but more and more fascinating to Nora.  When her translation of the letters leads to a new discovery, she never expects it to end with the professor insane, Chris dead, Adriane catatonic and Max gone and branded a murder...but that's what happens.