Lots of ways to make things faster and more efficient. If you're looking to use that ms timing counter as a number, then you should extract it as a field.
tstats will not give you data unless you're taking it from a datamodel, in which case, you will no doubt have extract fields by virtue of having passed it through the model.
Efficient searching is about taking the minimum amount of data to satisfy the search, so give as many restrictive criteria as possible, then aggregate to reduce the data volume as much as possible.
Dashboard efficiency can be achieved by using base searches
https://docs.splunk.com/Documentation/Splunk/9.0.1/Viz/Savedsearches
Another technique is to have a saved search that runs frequently and performs some aggregation of the large volume of data and then save that aggregated data back to a summary index and then your dashboard can search from the already created aggregations.
As for extracing those ms values at search time, here's an example that will extract all the (*_TT:NNms) fields from your example line
| makeresults
| eval _raw="2022-09-11 22:00:59,998 INFO -(Success:true)-(Validation:true)-(GUID:68D74EBE-CE3B-7508-6028-CBE1DFA90F8A)-(REQ_RCVD:2022-09-11T22:00:59.051)-(RES_SENT:2022-09-11T22:00:59.989)-(SIZE:2 KB)-(RespSent_TT:0ms)-(Actual_TT:938ms)-(DB_TT:9ms)-(Total_TT:947ms)-(AppServer_TT:937ms)"
| rex max_match=0 "\((?<fn>\w+)_TT:(?<tt>\d+)ms\)"
| foreach 0 1 2 3 4 [ eval f=mvindex(fn, <<FIELD>>), tt_{f}=mvindex(tt, <<FIELD>>) ]
| fields - fn tt f
The first two lines set up your example and the last 3 lines extract those numbers and create field names tt_XX where XX is the name of the time taken field and the value is the time excluding milliseconds.
