\[ y^{(3)}(x) \left (y'(x)^2+1\right )-3 y'(x) y''(x)^2=0 \] ✓ Mathematica : cpu = 0.246633 (sec), leaf count = 95
\[\left \{\left \{y(x)\to c_3-\frac {i \sqrt {c_1{}^2 x^2+2 c_2 c_1{}^2 x-1+c_2{}^2 c_1{}^2}}{c_1}\right \},\left \{y(x)\to \frac {i \sqrt {c_1{}^2 x^2+2 c_2 c_1{}^2 x-1+c_2{}^2 c_1{}^2}}{c_1}+c_3\right \}\right \}\] ✓ Maple : cpu = 0.424 (sec), leaf count = 49
\[\left \{y \left (x \right ) = c_{3}-\sqrt {-x^{2}-2 c_{2} x -c_{2}^{2}+c_{1}}, y \left (x \right ) = c_{3}+\sqrt {-x^{2}-2 c_{2} x -c_{2}^{2}+c_{1}}\right \}\]