Universal:
If you are staying onsite, in the morning, when it opens (whether it be Sunday or Monday) go on MIB with the FOTL. Even though you have FOTL, the MIB express starts to back up near lunch time. Go on as many times as you'd like in the morning (my parents and I go on at LEAST 3 times...get our share for the day...and come back maybe in the evening after Express dies down a bit).
Make sure to check out the Horror Makeup Show. This could be a nice "filler" in the day. A chance to sit down in the AC too. First show is at 11:45 usually and it's a good way to take a break from the heat for about 30 minutes.
Earthquake you can go to in the afternoon too. Use your FOTL because even though they take a LARGE amount of people at a time, the line does get backed up. With the FOTL, your in right when they let the next group in.
Back to the Future you can go anytime.
Islands of Adventure:
For Spiderman either in the morning or later in the evening, although this one doesn't usually get too bad...as long as you get FOTL. If you don't have FOTL go FIRST THING IN THE MORNING. I mean, as soon as the park opens. Don't even wait until the park has been open for 30 minutes. My friend and I were stuck with 75 minute wait in the morning once. It gets up to 2 hours sometimes.
I went on the Hulk around 6:00pm or later and had MAYBE 1 or 2 people in Express before me...I would always get on the next coaster! VERY nice. Sometimes, in the early afternoon there is a bit of a wait too.
On Popeyes you can either do in the afternoon when it is hot, or in the evening (around 6:30...7:00...). My parents went on Popeyes at 6:30 and could go on twice...without getting back in line (they asked to stay on, and the line was fairly short, so...they let them).
So, basically, if you have FOTL, go to US first. Do MIB, then maybe Back to the future, then Horror Makeup Show, then Jimmy Neutron, then Twister, then Earthquake.
Then, in the afternoon go to IoA and do Spiderman, Dr. Doom (always a short Express Line), Hulk, and then maybe Jurassic and Popeyes.
That's what I'd do, but it's up to you, and your taste in rides. I'm a thrill seeker so if you aren't, things will probably be a bit different...
Whatever you do, have fun! Don't spend all your time running around and make yourself exhausted. Make sure you really enjoy each moment. If you rush it all it'll be less than relaxing.