i waited two months before i offically put my two buns together. i had both mine fixed a male and female so their wouldnt be any hormones flying! And yes i did put both cages next to eachother and even had each of them sleep in the others cage to get used to eachothers sent. my male bun was calm and friendly but lady bun was kinda moody and didnt want to accept brownie. eventually they did accept eachother, and they love to snuggle with eachother!! THey now sleep in the same cage and enjoy good times.
I am sorry to hear that your buns did fight, just give them some time, if its meant to be its meant to be.
good luck to you!