Is there any point to begin wearing a chinstrap 13 days post surgery?

A chin strap provides needed support to the tissues during the healing process. I usually recommend patients wear it for a month, at least while sleeping or lying down. 

Having performed over 5,000 lower facelifts over the past decade, in my experience I would state that chin straps/neck garments do serve a purpose.  Many patients find that they reduce the swelling on a daily basis and also allow the new neck contour to heal evenly with less "lumps and bumps".  Many patients report that they wish they can wear it all the time for the first month post-procedure.  At our Center we recommend using the garment 10-12 hours daily for one month after the procedure.  This has worked well for us, and it is completely reasonable that your surgeon wants you to wear a garment postoperatively.

There is no harm that could be caused by wearing the chin strap 13 days after a facelift.  I typically only have my patients where the garment for 1-2 weeks after surgery.  It will depend on the nature and aggressiveness of the surgery.  If you surgeon has requested you to wear the garment after a facelift, I would follow his instructions.  I am sure he has a good reason.I hope this helps.  

Your surgeon is monitoring your healing.  For you best result follow his post operative instructions.  Best to you!