What is the max network latency between synchronous-commit AlwaysOn Availability Groups
There is no maximum for the supported latency for synchronous replicas.  You will sometimes opt for a higher-latency deployment in return for a RPO=0 for a broader range of failures.  

The most common mission-critical configuration is to have a pair of synchronous replicas on separate racks in the same datacenter, and a third, asynchronous replica in a separate datacenter.  

But guidance for your scenario should probably come from SAP, or from the Microsoft/SAP Engineering Alliance.  See eg https://techcommunity.microsoft.com/t5/running-sap-applications-on-the/bg-p/SAPApplications/label-name/AlwaysOn