Really? I mean, I can do one competition right away after the other. But that might be because I am only level 19 and maybe it doesn't work for really high levels. Oh, and I have to tell you guys that the time cheat does not work, it screws up you game. I used to be level 37 and then I used the time cheat and it screwed up my game so I had to restart and now it takes forever to complete everything.
I hate it. But anyway, you should be able to do another competition right after another.