You need paid build 0.4.6.1 to go inside the lab, to open it you need to do 3 quests for Yosuke
- attend Friday party
- meet with Yosuke at night the next day
- get nanotransistor from mad science student (I think it was during random events at school)
- wait for 2nd Friday party
- meet up with yosuke again at night to give him transistor and progress the quest
- cook pizza for him
- he will give you a key to unlock lab