I got my nucs a couple weeks before you did. One hive is building very fast, plenty of bees and I added a third box last Sunday. The other hive is working much more slowly. There doesn't seem to be as many bee. When I looked at the brood laid on new comb, it was very spotty. Today I went in and the pattern was much tighter with plenty of larva that'll be capped soon. I figure within 20 days, I'll have a population boom in that hive and it should really take off.
I'm suspecting that I lost a lot of brood from that hive during transport home and they're just now making up for it. I only found one queen cell with nothing in it. My only worry is since the queen seem to have waited so long to start laying, she may be a bit honey bound. The frames with the brood was about 2/3 nectar and honey and 1/3 brood. I gave them a few frames with started comb from the other hive to seed their top box. Since Sunday that built the started comb and even have capped honey but haven't started any new frames.
Tomorrow I'll break down the stronger hive to check the brood pattern. Hopefully it'll be solid and I'll spot the queen. I saw her Sunday for the first time, looked away for a second and she was gone. I don't know if the fell back into the hive, flew away, or blended in that well. There was a large bee buzzing by me a few times while I was putting it back together, but I didn't get a good look.