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EDIT: Never mind I found it. Within 28 days of application. Thanks!
state that in parent's noc letter
It is questionable whether you would be considered "living" in China if you were in the country on a visit visa, particularly if the UK government considered you living in the UK and only visiting China. If you are married, having lived together is not a requirement, so if the space is available it may be best describing it as you have here.
Depends on what you are using the entry/exit stamps for. Submitting the biodata pages for each of you is definitely necessary. The applicant is also usually required to list recent travel history, so including pages with entry/exit stamps is good supporting evidence of this. Including the entry/exit stamps of the sponsor can be used to help show a genuine and subsisting relationship where you have spent time in the same country together, so whether you include those is up to you depending on how you intend to show meeting that requirement.