In September, the busiest times for these parks will be the weekends when local people visit and people come for a weekend visit. That said, Universal CMs (not called that as they aren't Disney but you know what I mean!) still maintain that Sunday is a quiet day for them and most definitely Saturdays are the busiest.
I would always aim to get to parks for opening to get some rides under your belt before the main crowd arrives, I don't think Busch offers any type of Express ticket or Fastpass system - please someone correct me if they've recently introduced something similar - so worth arriving early.
Also with Sea World - Kraken, Journey To Atlantis and Wild Arctic are worth going on first thing before they get long lines.