Someone else asked a version of this yesterday with a 9:05 ADR. We always book a TH ADR for just after 9:00 park opening and we always enter early.
There will be a gate for early entry for character breakfast and it will have a sign that says "character breakfast" over it. You walk up to the CM at that gate, and they will get your name and check the list to verify you have an ADR and then they will let you through. You absolutely need to get in early for a 9:00 ADR, or you will be pretty late AND you need to get to the character breakfast gate MORE than 10 minutes before park opening. Because of the rope drop ceremony, they close the AK character breakfast gate around 10 minutes before park opening and then you will not get in until the rest of the crowd gets in the park. You will be in the regular lines to get in, caught behind the rope drop ceremony and possibly a good sized crowd and then you will smushed in with the portion of the crowd all heading to ride Safari while you are trying to get to TH. We made that mistake once. We actually saw them flip the character breakfast sign as we were walking up and they told us we were too late and would have to wait because of the rope drop ceremony. With the rope drop mess, we still got there right at 9:15 for our 9:15 ADR, but the people standing next to us had a 9:00 am ADR and they were 15 minutes late. We actually got a table before them as we checked in first, but we had about a 20 minute wait for a table because of the crowd of people caught behind rope drop. It was a big long line to check in, and then a wait to get seated. I would recommend getting there at least 15 minutes before the gate opens in case they shut it a little early.
To my knowledge the recommendation we have always received from WDW has always been to check in 20 minutes before our ADR (although we have checked in 5 minutes before plenty of times). As WDW states that they want you to check in 20 minutes before your ADR, so you will have no trouble getting in early. We usually enter at about 8:40 to 8:45 for our standard 9:15 ADR, and have never had any trouble getting in the gate at that time. We take a nice leisurely walk to TH. The photopass photographers are out and we get some nice pictures of us in front of the Tree of Life with no one else in them, on the way, and more often than not we get seated before our technical ADR time.
I believe that the reason those that have 8:00 or 8:05 ADRS are not let in until 8:00 a.m., is that TH does not open, and the first ADR is not, until 8:00 a.m. I don't believe they let you in the gate until the restaurant is actually open.
