If you haven't bought equipment, then it's too late now.
Lucky for you, defenders that are naked now get some basic peasant gear to defend themselves with. That is what you will have to use.
If you don't show up and the enemy shows up, you lose.
If nobody shows up, the defender wins.
Make a post for people to apply to your battle here:
http://forum.meleegaming.com/mercenary-recruitment/
The price to hire a commander is usually all your gold, equipment and looms in cRPG.
Joking. Just ask if someone can take charge if you're not there. People fight for XP anyway, so it will probably be fine. If nobody is actively leading the battle, people would still manage to get an idea or plan for what to do in the small preparation time, but since you are defending in peasant gear, you don't really got any other tactical choice but to camp you spawn/somewhere close to spawn (don't let them capture your spawn, btw). So just write that in the briefing and your players should know what to do.
Your main problem is that the battle is 7 AM on a Monday. Not many willing to fight then.