\[ -a x y'(x)+x^3+y'(x)^3=0 \] ✗ Mathematica : cpu = 299.997 (sec), leaf count = 0 , timed out
$Aborted
✓ Maple : cpu = 0.056 (sec), leaf count = 299
\[ \left \{ y \left ( x \right ) =\int \!{-{\frac {i}{12}} \left ( \left ( -108\,{x}^{3}+12\,\sqrt {-3\,{x}^{3} \left ( 4\,{a}^{3}-27\,{x}^{3} \right ) } \right ) ^{{\frac {2}{3}}}\sqrt {3}-12\,\sqrt {3}ax-i \left ( -108\,{x}^{3}+12\,\sqrt {-3\,{x}^{3} \left ( 4\,{a}^{3}-27\,{x}^{3} \right ) } \right ) ^{{\frac {2}{3}}}-12\,iax \right ) {\frac {1}{\sqrt [3]{-108\,{x}^{3}+12\,\sqrt {-3\,{x}^{3} \left ( 4\,{a}^{3}-27\,{x}^{3} \right ) }}}}}\,{\rm d}x+{\it \_C1},y \left ( x \right ) =\int \!{{\frac {i}{12}} \left ( \left ( -108\,{x}^{3}+12\,\sqrt {-3\,{x}^{3} \left ( 4\,{a}^{3}-27\,{x}^{3} \right ) } \right ) ^{{\frac {2}{3}}}\sqrt {3}-12\,\sqrt {3}ax+i \left ( -108\,{x}^{3}+12\,\sqrt {-3\,{x}^{3} \left ( 4\,{a}^{3}-27\,{x}^{3} \right ) } \right ) ^{{\frac {2}{3}}}+12\,iax \right ) {\frac {1}{\sqrt [3]{-108\,{x}^{3}+12\,\sqrt {-3\,{x}^{3} \left ( 4\,{a}^{3}-27\,{x}^{3} \right ) }}}}}\,{\rm d}x+{\it \_C1},y \left ( x \right ) =\int \!{\frac {1}{6} \left ( \left ( -108\,{x}^{3}+12\,\sqrt {-3\,{x}^{3} \left ( 4\,{a}^{3}-27\,{x}^{3} \right ) } \right ) ^{{\frac {2}{3}}}+12\,ax \right ) {\frac {1}{\sqrt [3]{-108\,{x}^{3}+12\,\sqrt {-3\,{x}^{3} \left ( 4\,{a}^{3}-27\,{x}^{3} \right ) }}}}}\,{\rm d}x+{\it \_C1} \right \} \]