I had a huge success with this in our recent June 18-25 trip for 4 people! These are the same-day FP+we snagged after using our initial three (we tried to move up the initial ones as we tap in, to be able to look for additional FP+ as much as possible:
Wed EPCOT - (RD Soarin', Initial 3 Spaceship earth, Mission space, FEA) + Test track 4:45
Thu Magic Kingdom - (RD Space mountain, Buzz, Initial 3, Pooh, Peter pan, 7DMT, other fantasyland rides in AM in standby) + Speedway 3pm, Barnstormer 3:20, Dumbo 3:40, It's a small world 4, Buzz 5:20
Fri EPCOT - (Initial 3 Test track, Seas with Nemo, Turtle talk) + Living with the land 11:30, Test track 2:15, Soarin' 6
Sat Animal Kingdom - (Initial 3, EE, Safari, FOP) + Kali 1, Dinosaur 2:20, Nemo 4 show, we kept trying for Navi but Navi was down in the AM for a while, and we couldn't find one.
Sun Magic Kingdom - (Initial 3 Splash, Big thunder, Haunted mansion) + Pirates 1:30, Jungle cruise 2:15, Aladdin carpet 2:40, Seven dwarf mine train 4:45
Mon Hollywood Studios - (RD TSMM, Initial 3: SDD, ToT, Star tours) + AS2 1:45, Toy Story Mania 3:30, Fantasmic 9 show, we kept trying for 2nd SDD but did't make it.
Overall, I was surprised how well it worked! The only time-consuming refresh (took me a 3-4 attempts to refresh for 2-3 minutes at a time) was 7DMT. Could not get Navi or FOP/SDD. Most we had to wait for a ride was Toy Story Mania in standby as we were late to rope drop (waited 30 min). I followed everyone' advice and grabbed the time available for ride we want and tried to move it forward. Only thing I had difficulty moving forward was 7DMT - that one, one we grabbed was the one we ended up using as no earlier time came along.