Night for Day by Roselle Lim

Two people destined to be together, but to never see each other again, fight against the greatest odds in this powerful and moving fantasy novel by critically acclaimed author Roselle Lim.
Exes Ward Dunbar and Camille Buhay thought they would never see each other again. They had broken up to pursue their dream jobs on opposite sides of the country-her to New York City, and him to Los Angeles. But years later, they unexpectedly reconnect in London, where they are interviewing for similar jobs. The spark they feel when they meet again is palpable-the attraction comes back like muscle memory, reminding them of what they had lost. When Ward and Camille discover they both got the job working opposing shifts, they vow to give their relationship another try.
Ward starts the day shift and finds the immortal clientele unusual and dazzling. When he clocks out at the end of the day, he finds the door locked and himself trapped in the building. After a horrific first night shift contending with restless spirits and ghosts, Camille is also unable to escape. In their respective prisons, they discover that they're able to talk to each other a few minutes before dawn. This fleeting encounter incites longing for each other, but their promise to be together feels impossible. Because they are caught in the middle of a war of the gods-and their choices will determine the outcome.