Same exact thing for us. I posted about this in another thread when someone asked if you can get refunded for Lightning Lanes that you can't make, but I'll add some details here, since there seems to be confusion on if the system holds your time or does not (spoiler: it does not) while you're checking out.
Saturday I purchased an Individual
Lightning Lane for Flight of Passage for 2:45-3:45pm. We had a reservation at Tiffin's for 4:20pm, so I figured that time would be perfect for us. I confirmed it and paid, but when it showed up in My Day it was for 4:15-5:15pm. Tiffin's takes a good 1-1 1/2 hours for a meal, so this time couldn't work. I thought maybe it changed and I didn't notice before I hit CONFIRM, so just saw Guest Services when I got to the park and they helped us out a lot and gave us a pass to use any time we liked for the ride. This helped immensely, since Flight of Passage was running at half capacity for most of the morning.
Sunday morning I woke up to purchase an Individual Lightning Lane for Rise of the Resistance for our group. My girlfriend and I had to leave the park by 5pm to catch a flight home, the other couple in our group could stay all day. I chose 12:30pm and was given a 1:25-2:25pm window on my confirmation screen. I made sure that it stayed that way through the whole confirmation because of what happened the day before. When it showed up in My Day it was for 3:25-4:25pm. I have the email receipt that is timestamped at 7:00am, so I took less than 1 minute to CONFIRM the time. We had Oga's at 2:50pm and know that Rise often goes down for long periods throughout the day, so we went to Guest Services again. This time we were told that Oga's has a 45 minute time limit and we could still get in line for Rise by 4:25, so try that and if the line is too long for us to ride it, then the couple staying at the park could stay in line and my girlfriend and I could come back and get a refund.
Everything worked out and we actually had 40 minutes left in the park after the ride, since it was basically Walk-On with the ILL. But, I do think when a particular time is sold to the guest, they should absolutely get the time they paid for, because it may not work out as well for other groups.
We actually used
Genie+ and Individual Lightning Lanes to our benefit during this trip, but I don't like the system or how it's implemented. We are more casual (don't care if we miss a ride this time) park-goers, so it was fine for us, but I couldn't imagine the stress this could put on a family.