To legally buy oxycodone online, you must have a valid prescription from a licensed healthcare provider and use a legitimate, accredited online pharmacy. It is important to avoid unverified sources, as they may sell counterfeit or unsafe medications. Always consult your healthcare provider before making such purchases. Buying oxycodone online means purchasing the prescription opioid pain medication via the internet. This requires a valid prescription from a licensed healthcare provider and should be done through accredited, legitimate online pharmacies to avoid legal issues, counterfeit drugs, and health risks. The depends on whether you are taking standard oxycodone capsules, tablets or liquid, or slow-release tablets. Standard oxycodone takes 30 to 60 minutes to work, but this wears off after 4 to 6 hours.