Solution (source code)

= Solution

At an interior maximum, $\dot E(t)=0$, equivalently
$$
q_{EI}e^{-q_{EI}t}=q_{SE}e^{-q_{SE}t}.
$$
Thus
$$
t_{\max}=\frac{\log(q_{EI}/q_{SE})}{q_{EI}-q_{SE}}.
$$
This is positive for distinct positive rates. Its continuous limit when $q_{EI}=q_{SE}=q$ is $1/q$.