How soon after upper eyelid surgery can I have ptosis repair?

By 4 months, the swelling associated with the blepharoplasty should have resolved enough for your surgeon to accurately assess your ptosis.I would recommend a consultation with an Oculofacial surgeon. I have posted a resource for you to find one near you in the link below

At around the 6 month mark would be a good time for an assessment. Please wait until then before considering revision surgery.

You should wait about 6 months to be sure that any swelling has gone away as this can make the lid droop.  At  6 months, a good option is then a Mullers muscle resection to elevate the lid.  This is a surgery that is done from the underside of the lid.  It is a great surgery for patients who do not need any skin removed. See an oculoplastic surgeon so they can do a special  test to see if you are a candidate for this surgery.  

It is not routinely repaired.  Sometimes swelling associated with the surgery can make the ptosis worse.  Sometimes it is simply that the blepharoplasty was unmasked by the blepharoplasty.  Generally by 4 months it is reasonable to have this surgically addressed.  As a practical matter, you may that by the time you find the right surgeon and get scheduled, you will be close to 6 months after your surgery, a time frame that most surgeons are comfortable with.

If ptosis has been unmasked by blepharoplasty and you desire it to be corrected this can be done at any time.