Hello kerryzhuang,
The Dictionary of the "Real Academia" says:
HABER DE + INFINITIVO: denota DEBER, CONVENIENCIA o NECESIDAD de realizar lo expresado por dicho infinitivo. Ex.: "He de salir temprano"; "Habré de conformarme".
So, essentially, your sentence is in PRESENT TENSE (but expressing a sense of future): "Cuanto tiempo ha de pasar" is very very similar in meaning to "Cuanto tiempo tiene que pasar" or "Cuanto tiempo es necesario que pase".
The translation given by Karen and Xanita could be right, but it depends on the context. For example, a possible translation could be "How long should it take...?". Imagine you're cooking and you ask somebody how long it should take for the water to boil: ¿Cuanto tiempo ha de pasar para que hierva el agua?
Many times, as here, it can additionally express a future action: Ex.: Ha de llegar un día en que...(the day will come when...).
Finally, in other contexts, "haber de" could also express probability: "Ha de ser tarde": "it must be late".