In Vipassana meditation - How long does one keep watching an object?

When doing vipassana meditation and when one is observing an object - for how long does one keep observing and noting the object? I have been wondering about this for a while now since i do not know what the "correct" approach is if such an approach exist. I have once read that one should keep observing the object until it ceases to exist in order to clearly see the dissolution-step of the process that all objects follow -> *Arising, Presence, Dissolution*. Thereby one will be able to see the impermanent nature of phenomena. Help would be much appreciated. Thank you. Lanka