\[ \boxed { {\frac {{\rm d}^{3}}{{\rm d}{x}^{3}}}y \left ( x \right ) -\lambda \,y \left ( x \right ) =0} \]
Mathematica: cpu = 0.017002 (sec), leaf count = 53 \[ \left \{\left \{y(x)\to c_1 e^{(-1)^{2/3} \sqrt [3]{\lambda } x}+c_2 e^{-\sqrt [3]{-1} \sqrt [3]{\lambda } x}+c_3 e^{\sqrt [3]{\lambda } x}\right \}\right \} \]
Maple: cpu = 0.015 (sec), leaf count = 53 \[ \left \{ y \left ( x \right ) ={\it \_C1}\,{{\rm e}^{ \left ( -{\frac {1 }{2}\sqrt [3]{\lambda }}-{\frac {i}{2}}\sqrt {3}\sqrt [3]{\lambda } \right ) x}}+{\it \_C2}\,{{\rm e}^{ \left ( -{\frac {1}{2}\sqrt [3]{ \lambda }}+{\frac {i}{2}}\sqrt {3}\sqrt [3]{\lambda } \right ) x}}+{\it \_C3}\,{{\rm e}^{\sqrt [3]{\lambda }x}} \right \} \]