How can I calculate the time taken to go from one point to another, in vertical circular motion? If we have radius, angle between 2 points, and initial velocity.

I tried to write $\frac{dv}{dt} = g \cos \left(\frac{vt}{r}\right)$, but I don't know how to integrate that. I also tried to write velocity as a function of $\theta$ using conservation of energy, but again was not able to get anything out of it.