Thief of Time by Terry Pratchett

Thief of Time is the 26th novel in Terry Pratchett's Discworld series, focusing on the concept of time itself, which is managed by the History Monks to ensure tomorrow always comes. The plot centers on the construction of the world's first perfectly accurate clock, which threatens to stop time completely, prompting Monk Lu-Tze, his apprentice Lobsang Ludd, and Death's granddaughter Susan Sto Helit to race to stop it. It's the fifth book in the Death sub-series but can be read independently.