  With recent advances in post-Newtonian (PN) theory and numerical relativity
(NR) it has become possible to construct inspiral-merger-ringdown waveforms by
combining both descriptions into one hybrid signal. While addressing the
reliability of such waveforms, previous studies have identified the PN
contribution as the dominant source of error, which can be reduced by
incorporating longer NR simulations. Here we overcome the two outstanding
issues that make it difficult to determine the minimum NR simulation length
necessary to produce suitably accurate hybrids: (1) the criteria for a GW
search is the mismatch between the true waveform and a set of model waveforms,
optimized over all waveforms in the model, but for discrete hybrids this
optimization was not yet possible. (2) these calculations typically require
that numerical waveforms already exist, while we develop an algorithm to
estimate hybrid mismatches errors without numerical data. Our procedure relies
on combining supposedly equivalent PN models at highest available order with
common data in the NR regime, and their difference serves as a measure of the
uncertainty assumed in each waveform. Contrary to some earlier studies, we
estimate that ~10 NR orbits before merger should allow for the construction of
waveform families that are accurate enough for detection in a broad range of
parameters, only excluding highly spinning, unequal-mass systems. Nonspinning
systems, even with high mass-ratio (q>=20) are well modeled for astrophysically
reasonable component masses. The parameter bias is only of the order of 1% for
total mass and symmetric mass-ratio and less than 0.1 for the dimensionless
spin magnitude. We take the view that similar NR waveform lengths will remain
the state of the art in the advanced detector era, and begin to assess the
limits of the science that can be done with them.
