I agree with pretty much everyone here that you should reach out to the Buyer once and ask them to consider a review revision before you leave your own. Explain that you delivered ahead of schedule within the purchased duration time (attach a screenshot showing this) and note how much reviews affect you as a Seller good or bad.
The important thing is that the review is actually accurate, in which case the Buyer’s is not if they stated it was late when it wasn’t.
If they say no, simply rate them accordingly to your own experience with them (you have this ability too, so use it) and explain in your review details that the order wasn’t late and was delivered ahead of scheduled well within the duration time or the advertised delivery.
Buyers aren’t going to shy away from you because you give a review with your own experience with a Buyer when they clearly stated something that is false and you have the backbone to rate them and address the issue professionally yet in a public manner.
If there was no discussion prior about the delivery time/date between you and the Buyer I might ask CS first about what you should do if the Buyer is stating false information in their comment. Not sure what they will say or do, but it doesn’t hurt to simply ask. Be sure to provide screenshots!