op. I think I am understanding you. 3 possibilities here. and focusing on hp lands only.
1. us has ee and opens at 7 for ee, and ioa opens at 9 as regular admission. no brainer, you start at us and do diagon alley and gringotts. after doing gringotts, you continue to do gringotts in single rider line. you can get in 4 or 5 rides before the masses get there. then take Hogwarts express to ioa, as soon as you can and do fj.
2. both parks have ee. so us opens at 7 and ioa opens at 8. not likely based on this time of year. so you do the exact same plan as for #1.
3. ioa has ee and opens at 8. us opens at 8 for regular admission. i would do gringotts first as those lines tend to be longer. then i would get on the Hogwarts express, to fj as soon as i could as many of the ee people in ioa will already be in line for kong and most of the masses coming in when it opens at 9 regular will go to kong first also keeping fj less crowded than it would normally be early.
hope this is what you are looking for.