Will my chin implant become less sharp and long? At least by 5mm?

You still have significant swelling of the chin and around the implant. It will take at least 3-6 months to get better idea about final shape and size of your chin.You seem to have a good report with your surgeon; follow her (his) recommendation. In the worst case scenario your implant can be exchanged in local anesthesia for different shape and size. Frequently with facial and other implants you do not know how much you  will like it until you have it done. Good luck.

 Hi, I have performed many facial shaping procedures, including Chin Augmentation with dermal fillers or silastic chin implants, for over 30 years.  A medpore chin implant becomes integrated into the bone, as early as 1 month post-op, making it very difficult to remove and replace with another implant in a different position on the chin.  While silastic chin implants can be easily removed and replaced...medpore implants can not.  At 9 days post op, the chin is still swollen, especially if the chin implants was placed through the mouth which requires a greater degree of soft tissue dissection.  You should discuss this with your Chin Implant Surgeon before the implant becomes integrated. When the chin is weak, this creates an imbalance making the nose appear larger, the mid face top heavy, the lower face looks short, de-emphasizes the lips and allows early formation of a "double chin".  
 Proper placement of a silastic chin implant adds forward projection to the chin thereby creating harmony and balance to the lower face.  Using the same incision, liposuction can be performed to reduce the fat and further shape the neck.  Excess skin, from below the chin, can also be removed through the same incision.  
 I have found that placement of a silastic chin implant, through a small curved incision under the chin (also allows excess skin removal) to be very safe, quick, highly effective and far less invasive than a sliding genioplasty (requires extensive tissue dissection, bone cuts and placement of metal screws and plates to secure the cut bone segments).  I perform chin implant surgery in 30 minutes or less, often using a local anesthetic alone.  Hope this helps