With lazy-build loading the computation for the estimated duration may become expensive:

• it searches of the last 3 unstable (or better) builds to compute the runtime.
  In the (not very probable, but still possible) that there are a lot of builds and less than 3 have been unstable, it can be very expensive to lookup the builds.

Limit the number to build to go back in time and maybe also consider failed builds in the calculation