Bikram Yoga Options

I know what Bikram Yoga is, 26 poses done in heat.

I know it has lots of physical benefits.

But does it have any (positive) impact on your workings with magick? (Apart from being fitter)

Or does it have any association at all?

With Bikram the idea is purification by heat, but this is also kind of dangerous.
Any time of Yoga will help you in your magic. It will help the energy flow better, open the chakras, and some Yoga (I don't know about Bikram) can slowly raise your Kundalini.
The biggest benefit from Yoga (And the original purpose of Yoga) is that your body stays healthy and is conditioned to sit for many hours in meditation-This will be a big benefit to your practice.
I recommend Iyengar, Integral, or Jivamukti.

Heat? What kind of heat are we talking about here? I know how extreme some people can get, but do you mean on a typical hot summer day?