Lower Eyelid Drooping After Blepharoplasty, How Long Should I Wait to Fix it?

This problem must be approached individually.  Treatment depends on the degree of eyelid malposition, whether or not there is lagophthalmos, what symptoms you are having, what the trend is over time, how bad it looks, and how you feel about it.  Tarsorrhaphy, suggested as a possibility by your surgeon, is a good temporary solution.  Corticosteroid injections, massage, and surgical revision (usually a minor office procedure) are other treatments.  Sometimes, spontaneously resolves as orbicularis tone recovers and edema (swelling) resolve.

You did not provide us a photograph.  There is more than one thing that can go awry with lower eyelid surgery.  "Putting a stitch in the eyelid" seldom corrects the problem.  It is understandable that the surgeon wants to take care of this issue as rapidly as possible for you.  However, it does not benefit you to have a fix that does not really help.  I agree that a second opinion is a good idea.  If you want to maintain your relationship with your surgeon, consider having them arrange  a second opinion with an oculoplastic surgeon they work with.  Generally it is best if you allow the eyelid to heal for an extended period of time.  This allows for a more precise correction.  Also some issue do settle down with a little time.  Please consider reposting your questions with photographs.