This is entirely up to you and your surgeon. Some people have both knees replaced at the same time. Others wait anywhere from three weeks to three years or longer.
Your decision may be based on some personal factors. For example if you have both knees done at the same time, is there someone who can help you at home for a few weeks after the operation? This is very important.
How is your overall health? Can you withstand two replacements at the same time or two major operations in the same month? Same year?
Is one knee much worse than the other or are they pretty much the same in terms of pain, stiffness, and loss of motion? Some patients choose to have the worst knee done first. They depend on the “better” knee during rehab. When the first knee replacement can support them, then they have the second knee done.
Talk to your doctor about his or her suggestions for you.