  We derive an identity relating the growth exponent of early-time OTOCs, the
pre-exponential factor, and a third number called "branching time". The latter
is defined within the dynamical mean-field framework, namely, in terms of the
retarded kernel. This identity can be used to calculate stringy effects in the
SYK and similar models, we also explicitly define "strings" in this context. As
another application, we consider an SYK chain. If the coupling strength $\beta
J$ is above a certain threshold and nonlinear (in the magnitude of OTOCs)
effects are ignored, the exponent in the butterfly wavefront is exactly
$2\pi/\beta$.
