  We investigate the infinite temperature dynamics of the complex
Sachdev-Ye-Kitaev model (SYK$_4$) complimented with a single particle hopping
term (SYK$_2$), leading to the chaos-to-integrable crossover of the many-body
eigenstates. Due to the presence of the all-to-all connected SYK$_2$ term, a
non-equilibrium prethermal state emerges for a finite time window
$t_{th}\propto 2^{a/{\lambda}^{2/5}}$ that scales with the relative interaction
strength $\lambda$, between the SYK terms before eventually exhibiting
thermalization for all $\lambda$. The scaling of the plateau with $\lambda$ is
consistent with the many-body Fock space structure of the time-evolved wave
function. In the integrable limit, the wavefunction in the Fock space has a
stretched exponential dependence on distance. On the contrary, in the SYK$_4$
limit, it is distributed equally over the Fock space points characterizing the
ergodic phase at long times.
