Use this:
http://www.universalorlando.com/Resort_Information/theme_park_hours.aspx
You can gauge crowd size by park hours
5pm park close: Happens for
HHN or special events only
6pm park close: low crowds
7pm park close: "normal" light-moderate crowds
8pm park close: moderate-heavy crowds
9/10/11pm park close: heavy/very heavy crowds
Also, for a month-to-month breakdown:
January: SLOW. Only busy New Year's week & MLK weekend
Feb: Depends on Spring Break & Mardi Gras setup. Usually slow-moderate
March: see Feb
April: Moderately busy, with super busy during Easter/Spring Break
May: Moderate until Memorial Day, then busy
June: Busy
July: Very Busy
August: Very Busy at first, Moderate by mid-Aug
Sept: Moderate-Busy for Labor Day weekend, then SLOW.
Oct: Slow/Moderate during the day. BUSY for HHN
Nov: SLOW. Busy Thanksgiving Weekend
Dec: SLOW. Moderate around Christmas. Very Busy 12/26-12/31