The Rellekka Rooftop Agility Course is available to players with an Agility level of 80 or higher. At 85 Agility players stops failing at the first tightrope and at level 89 second leap gap too, thus never failing on the course.
A full lap of this agility course can be done in roughly 51 seconds, making the maximum amount of experience possible 55,052.4 XP/hour assuming perfect laps. Keeping this rate is very difficult to achieve and a player should rather count on getting around 50k XP/hour.
Using this course alone, levelling up from level 80 to 90 would require 4308 completions of the course, meaning roughly 61 hours of training at the maximum hourly rate.