Morad noticed that the post-starburst galaxy images up at today's research page (named "SDSS_J01*.jpg") comprise a close pair, from which we can derive a timescale. I also noticed that this galaxy (below) is the highest luminosity galaxy in Blanton's "lowz" sample with a K+A nucleus. Nice interaction! (The circle has a radius of 100 h-1 kpc.)
In both of these cases, it is plausible that we will be able to estimate a timescale that is good to a factor of a few; the first with the crossing time, the second with the dynamical time times the number of visible loops. Email from Scott Tremaine a few days ago was pessimistic in the latter case.