I have a performance and need to make two quick changes. How should I manage that?

My band/choir concert is on Sunday, and I'm in three different acts that all have three different costumes. Unfortunately, these acts are all back to back, and it will be very hard because I'll only have 30 seconds tops to change in between. I start with choir, then go to band, then I have my a cappella group after band. For choir, I can just wear my robe over my band dress and take it off later, but the trouble is between band and the a cappella group, because I have two different dresses. I had originally intended to just wear my band dress over the other dress and just take off the band dress, but it's hard to get in and out of, and I'll have to deal with putting instruments away and switching all my music around. I'm wondering if there were a way to work out my quick changes so they would be easy to do. I tried asking my band director if I can just wear my a cappella dress for band because the two dresses are the same color, but he said no. I'm just nervous that I'll be late and miss one of my acts! How can I make my quick changes as easy as possible so I'm not nervous or pressed for time?