How long after a pneumothorax can I return to work?

Depends on work. As long as you are not breathing hard or lifting heavy objects you may return when breathing is comfortable. Wait 6 weeks at least for healing before anything strenuous and have a follow up x-ray before that time has passed to make sure the lung is fully inflated.
6?weeks. Varies first, no complications not from COPD or other lesions. X-ray back to baseline. Start slow and work up.