This requirement refers to your system, not to external integrations.
Basically, you are presented with the requirement: make sure you can deliver 5s or less on calls between request and response to your application
To tackle this requirement, you should consider multiple load balanced application server nodes, possibly with nodes dynamically allocated if demand surges (hardly achievable on physical nodes, but works well with cloud-based ones).
Also common tactics to address performance are using cache, increase throughput between nodes, use parallel rather then sequential calls where possible, using async calls.
SCJP5 | SCWCD5 | SCBCD5 | OCMJEA6
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