The same method that counts down can be modified to count up instead. It likely is just a matter of changing a - to a +.
Install OnTimerScript can be set up to run a script on a regular interval as frequent as 1 second. The two scripts might look like this:
Set Variable [ $$Start ; value: Get ( CurrentTime ) ]
Set Variable [$$Timer ; value: 0 ]
Install OnTimer Script [ UpdateTimer ; 1 ]
Update Timer script:
Set Variable [$$Timer ; value: Get ( CurrentTime ) - $$Start ]
Refresh Window --> this step may or may not be needed, experiment and see
You then put $$Timer on your layout as a merge variable (See Insert menu) and use data formatting to format it as time with desired time format.