The wait times in TouringPlans are based on statistical analysis and are captured in hour-by-hour wait forecasts that you can find for each attraction. Because the forecasts are hourly, it appears they interpolate wait times between hours. So for a certain date it may be that if you arrive at TP just a little after the park opens your expected wait is 10 minutes, but if you get there an hour after open it is 40 minutes. The forecast then assumes that the wait time behaves linearly in between those times, so it will indicate a wait time 25 minutes (halfway between 10 minutes and 40 minutes) if you arrive 30 minutes after park opening. The reality is probably that the wait time increases more rapidly than that in the first hour after RD.
The forecasts for ETWB tend to indicate a sharp rise in wait time in the first hour, followed by a gently crowned "hill" throughout the day (maybe 10-15 minutes variation) until around 8 p.m. then a gradual taper to park closing. This indicates, consistent with what others have said, that if you aren't one of the first in line, your wait at most points throughout the day will be similar. Some have recommended strategies that involve getting to ETWB a little after an hour following park open (the initial crowd has waned and the "late" crowd hasn't picked up yet) or going during afternoon parade or dinner time. TP doesn't show any lulls during these periods, but that doesn't mean they don't happen. Again, this is statistically based, and there is not but a few months of data based on actual experience with this attraction. However, if you buy that after the first hour the wait will be similar at most other times of the day, that means make sure you get there first or fit it in another time when you couldn't get as much done visiting other attractions. The first part is why others advise not getting FPs for anything else before you get there. Also consider the speed of your group and whether you have to park a stroller before getting in line as that could make a difference. The second part is why TP can list it 6th, 7th, or later and not affect total wait time much -- it's getting you to other things to save you more time there knowing it isn't sacrificing as much time by waiting on ETWB.
To see specific day forecasts for an attraction in TP.com go to the page for the attraction you want to see (you can get there by going to any of the park pages, click on "Attractions" on the left and then select from the list). Once at the page for the attraction click on "View Full Forecast" on the right side of the page under Current Wait Time. Above the chart is a link to view the next days forecast. If you click that it will advance to the next day. The web address for the next day includes the date at the end, so you can go to the web address and pick whatever date you want to see a forecast for that day.
Hope this is helpful.
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