April 16th: Yosuke awakens his Persona, Jiraiya. You'll gain access to the Velvet Room and Igor's services, including Persona fusion. This is a crucial mechanic. Spend some time understanding it. You'll also meet Margaret, Igor's assistant. You can now freely enter the TV World from Junes.
April 17th: Chie awakens her Persona, Tomoe. The three of you officially form the 'Investigation Team'. You'll be able to explore the TV World more thoroughly. Your first dungeon, Yukiko's Castle, is now accessible. It's recommended to start exploring it today if possible.
April 18th - 20th: Focus on exploring Yukiko's Castle. The deadline for this dungeon is April 29th. Try to clear it in one or two visits to save time for Social Links later. Remember to exploit weaknesses and use All-Out Attacks. Fuse new Personas in the Velvet Room to expand your combat options. Stock up on healing items from the Shiroku Store before entering the dungeon.