Strange Pathways for Black Hole Formation
  Immediately after they are born, neutron stars are characterized by an entropy per baryon of order unity and by the presence of trapped neutrinos. If the only hadrons in the star are nucleons, these effects slightly reduce the maximum mass relative to cold, catalyzed matter. However, if stangeness-bearing hyperons, a kaon condensate, or quarks are also present, these effects result in an increase in the maximum mass of up to $\sim 0.3{\rm M}_{\odot}$ compared to that of a cold, neutrino-free star. This makes a sufficiently massive proto-neutron star metastable, so that after a delay of 10--100 seconds, the PNS collapses into a black hole. Such an event might be straightforward to observe as an abrupt cessation of neutrinos when the instability is triggered. 
M. Prakash