Instead of limiting the tyers limit the amount of time for the sign up.My opinion is that two days is plenty of time for people who are interested in a swap to sign up. When my swap comes up I'll limit the time,not the # of tyers.If 20 sign up deadline for shipping is 20 days,25 sign up ship in 25 days.You have to average a jig per day to make it on time.That should be plenty of time.