I live in Iowa...our heat index because of humidity is regularly 10-20 degrees above actual temp. In July, heat indexes of over 100 are not unusual.
Now what got me and my husband on our honeymoon in 2015 was that we went in January at it hit 95 several days we were there. Our bodies were in complete shock and both of us got heat exhaustion at Universal. I think in July, it wouldn't be quite the shock, although I might be fooling myself
Back to OP question...my mom and I went this February, and it was an art festival day. We got in line for FEA at about 9:15 am and only waited about 20 minutes. Also, later in the day, there were FP available for the evening. So if you use all your FP in morning, you may be able to snag FPs for FEA in the evening. Otherwise, wait until Illuminations starts and hop in line. It appeared to be lower then.