Skipshock, by Caroline O'Donoghue

Traveling alone on the train from Cork to Dublin, Margo nearly passes out and suddenly finds herself in another world.  In danger from the very start, a trader named Moon rescues her and smuggles her off the train at their next stop. Margo learns that she has been transported from Ireland to a universe where multiple worlds exist, each one with a different length of day.  The most desirable southern worlds have 24-hour days and the least (and northernmost) have days as short as two hours.  Travel on the trains (the only remaining way to get between worlds) is strictly controlled and northerners are largely cut off altogether.  Unrest is everywhere.

Margo and Moon learn that her arrival is not entirely coincidence.  Margo is carrying an antique watch that once belonged to her late father.  In ways that they do not fully understand, Margo and the watch have the power to disrupt travel -- a power that the south desperately wants to have.  Chased between worlds, the two of them must unlock the mystery while evading capture.  All around them the old order is disintegrating and inter-world revolution is brewing.

A feisty adventure fantasy with a dash of romance.  I liked the role of day length as a world-builder and there's some thought given to how shorter days (and shorter lifespans would affect a world).  The author does great exposition, but the pace is so fast that things get destroyed as fast as they get introduced.   At the same time, there's a fairly large number of characters and a high body count. Hopefully, the planned sequel will explore some of the unfinished business instead of creating more stuff.  The pace flags at times as characters get involved in lengthy conversations. This is not a story that benefits from chit chat.