Dd was 10 week early so very tiny at 8 weeks when she first slept 12 hours! By chance she had an appointment with her consultant the next day so asked him if I should be wakening her to feed, he said def not just enjoy it as long as she kept putting on weight. She did and 3 years later I could count on one hand the nights she didn't sleep 12 hours.
The usual advice is to allow them a 6 hour stretch at night before waking them. I wouldn't worry about a 7 hour stretch.
The one piece of advice I'd offer is to make sure you wake them for a feed at 10 or 11, so as they get older their long stretch of sleep coincides with yours! We didn't do that with DD and she fed at 4am till she was nearly 2 (I know, I know, bad parents!) but we woke DS for a dreamfeed every night at about 10:30 and it meant he went through till the morning then, so we had much better sleep and his whole babyhood has been much less exhausting than DD's.