DBS wait time as shown in UTY6647, UTY6648 and UTY6649 messages is the wall clock time between the submittal by TPump of a request and the receipt by TPump of the response. Note that if the DBS is faster than TPump, the time will be longer than reality, since the response will be ready before TPump can actually receive it.
This information is tracked for each session/request, the submittal time of the current in-process request and then capturing the time when the response is received and taking the difference. The intent of keeping track of DBS wait time is to observe anomalies; it would be very useful to know if the slowness is due to a single session or request or to a general sluggishness.