  Recent observations of short gamma-ray bursts (SGRBs) suggest that binary
neutron star (NS) mergers can create highly magnetised, millisecond NSs. Sharp
cut-offs in X-ray afterglow plateaus of some SGRBs hint at the gravitational
collapse of these remnant NSs to black holes. The collapse of such
`supramassive' NSs also describes the blitzar model, a leading candidate for
the progenitors of fast radio bursts (FRBs). The observation of an FRB
associated with an SGRB would provide compelling evidence for the blitzar model
and the binary NS merger scenario of SGRBs, and lead to interesting constraints
on the NS equation of state. We predict the collapse times of supramassive NSs
created in binary NS mergers, finding that such stars collapse $\sim10\,{\rm
s}$ -- $4.4\times10^{4}\,{\rm s}$ (95% confidence) after the merger. This
directly impacts observations targeting NS remnants of binary NS mergers,
providing the optimal window for high time resolution radio and X-ray follow-up
of SGRBs and gravitational wave bursts.
