If it is early in your trip, you could have trouble. We have not had trouble getting ADRs toward the end of our trip for BOG, but we have not been able to get them early in the trip. It just depends on how many people start booking with their 180+ 10 for that date before it is your day to book. You might get lucky and get one for that trip. We have eaten at BOG at around 5:00 on a party night and been fine, but we went to 2 parties that trip, and gave BOG bigger priority than meeting some of the most popular characters on one of our party nights. If meeting the most popular party characters such as the 7 Dwarves or as of last year Jack Skellington is important to you, then you want to be in line for one of them by around 5:30 or 5:45 or else you will spend a good portion of you valuable party time standing in line. I would say go for a 4:00 or no later than 4:30 if you want to try to meet either of those. 4:30 would be cutting it close for those. If those characters are not important to you, but others are, there are also some other popular characters that getting in line before the party would be good such as meeting the Princes with their Princesses, but you don't have to be in those lines quite as early.