First you will visit the convenient store in the morning when Yui and the big guy are talking. Do this until you get a pop up massage.
After that at 00:00 till 02:00 (Not including) you will see in the Construction site at the top left of the map shadow figures.
Now to get the scene to happen, the steps are as follows:
- When you're in the construction site fast forward the time until 02:00 and Yui will bump into you.
- Do this 2 more times (3 time in total).
- At the 3rd time call her by her name when she bumps into you.
- Do step 1 again but this time don't forward time just talk to the shadows, when you do this Yui will let you join them.
After this you can come to the construction site anytime you like to revisit the scene.