\[ \boxed { {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) +5\,a{\frac {\rm d}{{\rm d}x}}y \left ( x \right ) -6\, \left ( y \left ( x \right ) \right ) ^{2}+6\,{a}^{2}y \left ( x \right ) =0} \]
Mathematica: cpu = 2.182777 (sec), leaf count = 31 \[ \text {DSolve}\left [6 a^2 y(x)+5 a y'(x)+y''(x)-6 y(x)^2=0,y(x),x\right ] \]
Maple: cpu = 0.016 (sec), leaf count = 27 \[ \left \{ y \left ( x \right ) ={\it WeierstrassP} \left ( -{\frac {{ {\rm e}^{-ax}}}{a}}+{\it \_C1},0,{\it \_C2} \right ) \left ( {{\rm e}^{ -ax}} \right ) ^{2} \right \} \]