When can I do hot yoga and/or High Intensity Interval Training post-breast reduction? (Photo)

The best resource of information would be your surgeon as each has his/her own protocols. There really isn't a standard time to return to activities, as each individual heals at a different rate. Generally, however, it is usually advisable to avoid strenuous activities for the first month post op, to allow early healing, and gradually return to activities. 

Thank you for the question and congratulations on having undergone the breast reduction surgery;  it is one of the most patient pleasing operations we perform. 
Generally, it is best to follow your surgeon's  guidelines in regards to return to activity/ exercise. Most of my patients are able to return to  lower body exercise (for example stationary bicycle)  two weeks postoperatively and return to vigorous activity about 4 to 6 weeks after the breast reduction surgery. 
My best advice: start slow and listen to your body as you gradually return to full activity. Best wishes for an outcome that you will be very pleased with.