Current pax-web undertow does not support(1) start-time option for it's access logging. So user can not log time taken to process the requests in milliseconds.
This is a knowledge article for EAP.
https://access.redhat.com/solutions/2172691
Karaf user needs a same option too.

(1)
https://github.com/ops4j/org.ops4j.pax.web/blob/master/pax-web-undertow/src/main/java/org/ops4j/pax/web/service/undertow/internal/ServerControllerImpl.java#L566-L585