> should I be concerned
Nope! :-)
Years ago I had a litter of 7 (apologies to those who have heard this before), first pup opened eyes on day 11, a couple 2 days later etc. etc. Until day 17 when one pups eyes remained firmly closed.
Naturally, bythis time, I had gone through every scenario in my head, with the final thoughts being that, when eyelids opened, there would probably be no eyes, and pupster would have to be PTS.
I made an appointment for the vet after work. Raced home from work, and picked the pup up, and lovingly kissed him on the nose. He opened his eyes widely. Blinked. And said
Gotcha!!PS (he didn't really speak.) :-) :-)