When do kinetochores attach?
Kinetochore (KT) is a multilayer protein complex. It's main function is to link chromosomes to the positive ends of the spindle microtubules. Also it plays role in the formation of heterogenic region at and around the centromer. The attachment of the KT is not uniform among living species. According to this paper on KT assembly in yeast:


  .  ...  KTs  remain attached to the MTs throughout the cell cycle in this organism. However, a temporary detachment of chromosomes  from  MTs  occurs  (for  1–2 min)  at  the  time of CEN DNA replication in S phase in S.cerevisiae (Kitamura et al. , 2007). After completion of CEN replication, a KT reassembles and reestablishes its attachment with  MTs.  


source:http://femsle.oxfordjournals.org/content/femsle/338/2/107.full.pdf
(CEN - centromere, MT- (spindle)microtubules)

Thus the exact time of kinetochore attachment depends on the organism, though I must note that S. cerevisiae has somewhat different mitosis than us.