You can follow this checklist before the theme is announced, every item should reduce the time scambling in the first 24 hours.

Team & Roles

• Recruit a team (1–4 people)
• Assign roles: programmer, artist, designer
• Define one decision maker per discipline
• Set a communication channel (Discord, in-person, whatever.)
• Set expectations: sleep schedule, crunching, skill levels

Tooling

• Select the game engine and project template
• Maybe prepare a repo or version control (when sharing is required, when your solo remove this)
• Art tools installed and tested (For example: Photoshop, Blender, Krita)
• Audio tools installed and tested (For example: FLStudio, Audacity, sfxr)
• Project board set up (Trello, Notion or a very simple shared text file in Git does the job also well)
• Everything launches and compiles, there should be no setup surprises on day 1

Scope Preparation

• Pre-define your cut list: features you’ll drop first under time pressure
• Set your Definition of Done: playable, coherent, communicates the core idea
• Choose a backup concept in case the theme clashes badly

Mental Preparation

• Weekend schedule cleared
• Food/snacks prepared in advance
• Sleep schedule set (6h minimum recommended)