There is an API available for ANTS which can mark regions on the timeline: see 'adding custom event markers' here
for details. Once the regions are marked, you can just select those relating to the tests you're interested in.
However, this is probably unncecessary for unit tests: as these are implemented as individual methods, you can just select the relevant method in the list. ANTS will draw a green bar on the timeline to show the times when the method was running, and you can click on this to inspect what was going on during that time. The call graph is also very useful for inspecting how an individual method is behaving.