They might think about time entirely differently from us--as something that comes from people. With no non-living examples of predictable change (assuming there are no cyclical weather patterns or seasons as well as no day/night cycle), these people might talk about time the way they talk about feelings e.g. "Gathering nuts takes a long time because it's boring." Standard time might be first tied to growing trees, which get obviously and predictably taller. Maybe every tribe has a "clock tree" it uses to make sure everyone has the same referent.

They might think about time entirely differently from us--as something that comes from people. With no non-living examples of predictable change (assuming there are no cyclical weather patterns or seasons as well as no day/night cycle), these people might talk about time the way they talk about feelings e.g. "Gathering nuts takes a long time because it's boring." Standard time might be first tied to growing trees, which get obviously and predictably taller. Maybe every tribe has a "clock tree" it uses to make sure everyone has the same referent. If you want time cut into pieces smaller than "growing a tree," perhaps they could measure time by heart beats or eye blinks (depending on their anatomy) how long it takes to get hungry after eating again, and how long it takes to gestate a child (or incubate one or whatever). More accurate and precise water clocks or candle clocks (or indeed clockwork clocks) won't be technically any harder for them to produce than they were for us, but I bet the inhabitants of this world will take longer to develop accurate and precise timekeeping, since they'll start from the assumption that time governs only earthly things, rather than heavenly.