Depending on how long it takes to get a tram , how long it takes for a monorail to show up (I advise skipping a long line and take the resort monorail if the regular line is outrageous.)and how far back you are in line for said monorail or boat,I think 8 AM is a better option for you. it will take 30 minutes to park, catch a tram and a monorail and arrive , get through bag check, and get through a turnstile. You are pushing it in my opinion with an 8!5 arrival. Not to mention if you do make it, you will be in the back of the rope drop crowd, which frankly could be a couple thousand people.
We like to be standing at the rope at LEAST 30-45 minutes before RD to make it count.
I have had ONE epic recovery from a later RD arrival, Starting OUTSIDE of the turnstiles, and Sprinting (I mean SPRINTING) down main street, and hooking a right through the terrace to land at the front of the second rope at Tomorrowland. Its nothing I ever (especially at age 53) want to have to repeat.