G+LL seem to be available most of the day for most attractions. Space Mountain and Indy push out somewhat quickly, but not terribly quickly.
For ILL, ROTR does regularly sell out by/before mid day. The others (WS/RSR) typically remain available. Keep in mind that these three attractions are ala carte purchases and NOT included with G+.
If attractions are your thing, it is worth it. On the surface, it works as advertised. If you are willing to spend more time on your phone you can min/max it by using the refresh trick as well as fishing for MEPs (Multiple Experience Passes are often given when you have an attraction booked that goes down). Using these two "advanced" techniques can help you reduce your wait between attractions as well as give you a way to ride your favorites more than once.