How hard will it be to secure FP's for big rides the week of arrival???

[edk35]

I am trying to figure out our tickets. We have a trip planned the week of Aug. 10th. We might wait until we arrive to get tickets at Shades of Green. Are our chances of getting FP's to the Mine Train ride, Soarin, Test Track, the big names… going to be impossible to get that late??? Thanks