\[ y'(x)=\frac {\left (4 a x-y(x)^2\right )^3}{y(x) \left (4 a x-y(x)^2-1\right )} \] ✓ Mathematica : cpu = 1.82677 (sec), leaf count = 89
\[\text {Solve}\left [2 a \left (x-\frac {\text {RootSum}\left [-\text {$\#$1}^3+2 \text {$\#$1} a-2 a\& ,\frac {\text {$\#$1} a \log \left (-\text {$\#$1}+4 a x-y(x)^2\right )-a \log \left (-\text {$\#$1}+4 a x-y(x)^2\right )}{2 a-3 \text {$\#$1}^2}\& \right ]}{2 a}\right )=c_1,y(x)\right ]\] ✓ Maple : cpu = 27.023 (sec), leaf count = 229
\[ \left \{ \int _{{\it \_b}}^{x}\!-{\frac { \left ( 4\,{\it \_a}\,a- \left ( y \left ( x \right ) \right ) ^{2} \right ) ^{3}}{- \left ( y \left ( x \right ) \right ) ^{6}+12\,{\it \_a}\,a \left ( y \left ( x \right ) \right ) ^{4}+ \left ( -48\,{{\it \_a}}^{2}{a}^{2}+2\,a \right ) \left ( y \left ( x \right ) \right ) ^{2}+64\,{{\it \_a}}^{3}{a}^{3}-8\,{\it \_a}\,{a}^{2}+2\,a}}\,{\rm d}{\it \_a}+\int ^{y \left ( x \right ) }\!{\frac { \left ( -{{\it \_f}}^{2}+4\,ax-1 \right ) {\it \_f}}{-{{\it \_f}}^{6}+12\,{{\it \_f}}^{4}ax-48\,{{\it \_f}}^{2}{a}^{2}{x}^{2}+64\,{a}^{3}{x}^{3}+2\,{{\it \_f}}^{2}a-8\,{a}^{2}x+2\,a}}-\int _{{\it \_b}}^{x}\!-4\,{\frac { \left ( 4\,{\it \_a}\,a-{{\it \_f}}^{2} \right ) ^{2}{\it \_f}\,a \left ( 8\,{\it \_a}\,a-2\,{{\it \_f}}^{2}-3 \right ) }{ \left ( 64\,{{\it \_a}}^{3}{a}^{3}-48\,{{\it \_a}}^{2}{{\it \_f}}^{2}{a}^{2}+12\,{\it \_a}\,{{\it \_f}}^{4}a-{{\it \_f}}^{6}-8\,{\it \_a}\,{a}^{2}+2\,{{\it \_f}}^{2}a+2\,a \right ) ^{2}}}\,{\rm d}{\it \_a}{d{\it \_f}}+{\it \_C1}=0 \right \} \]