JMHO, but we stayed at Nickelodeon in April, and we all thought it was absolutely gross, including all 4 of my children. The room was marginally clean with a toilet that didn't work (even though we called for maintenance 3 times). The people staying there for the most part were questionable (completely disregarding posted rules, despite being politely "reminded" - repeatedly - by the staff...and worse, some hot tub behavior that was to say the least, NOT PG...again, with a total lack of regard for the fact that the place was mainly populated by children).
Never again would I stay there, nor would I recommend it. I don't know about the time period you are inquiring about, but honestly, it wouldn't matter what time of year to me. Just yuck.