<p>I have a object to print for which I want the base to be printed very rapidly because it's just a cube but as the print reached around 70 % a complex circular structure needs to be printed at a slower speed. Is there any way I could control the speed at the given percentage of job done?</p>
<p>I want the cube to be printed at 50 mm/s and the complex circular structure at 40 mm/s.</p>
<p>Printer Type - FDM</p>

Simplify3D
has the ability to create more than one process, to be applied to the model at specific layers. It appears that feature fits perfectly with your requirements. As an example, you might create a process within S3D for layers 1 to 500 at the desired 50 mm / sec along with any other modifications you wish. The second process would specify layers 501 to 800 to be printed at 40 mm / sec.
The preview mode of S3D allows you to identify layer numbers in order to provide the necessary precision.