How early should travelers set up Alipay and Weixin Pay before China?

There is a due-diligence step by law, which is the real reason to set up before you fly

Article 21 obliges the institution to identify and verify your identity and to understand your transaction background — a process, not a checkbox. Doing it on hotel wifi the night before you need to pay is the same work under worse conditions, which is the practical argument for doing it at home while your usual bank contact is reachable.

Where in the source: 第二十一条: 建立持续有效的用户尽职调查制度，按照规定识别并核实用户身份，了解用户交易背景和风险状况.

Declining a data permission may not cost you the service, unless the data is necessary to provide it

Article 32 bars an institution from refusing service because a user declines or withdraws consent to information processing — except where that processing is necessary to provide the service. Worth knowing during setup: a permission prompt is not automatically all-or-nothing, though verification data itself will be necessary.

Where in the source: 第三十二条: 不得以用户不同意处理其信息或者撤回同意等为由拒绝提供服务，处理相关信息属于提供服务所必需的除外.

Sharing your data with an affiliate needs its own separate consent

The same article requires the institution to name the affiliate and its contact details and to obtain the user's separate consent covering what is shared, why, for how long, how, and with what protection. So a single sign-up tap is not consent to everything downstream.

Where in the source: 第三十二条: 与关联公司共享用户信息的，应当告知该关联公司的名称和联系方式，并就信息共享的内容以及处理目的、期限、方式、保护措施等取得用户单独同意.