The 90 day window out is exactly that...90 days from the date, in your case the 4th. July 4th is a biggie so I'd be on the phone no later than 6:55 to start my call in for PS.
As noted above, the 90 days is 90 days before the date you want to book for, not your check in date.
Here is a link to the Dis's PS calculator. http://www.wdwinfo.com/wdwinfo/dining/pscalc/dispscalc.html
If you plug in the date you want to book for, it will show you when that day, but only that day(and sooner of course), can be booked.
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