Player-1
Smash Legend
it's a 10 frame window to buffer 3 inputs since that's brawl's buffer time, but each character has an interrupt window on their dash attacks which is why there are different timings for DACUS. I'm not 100% sure if the interrupt windows affect bdacus, but I'm pretty sure they do.
You'll have to experiment with the timing yourself since it's hard to explain but the input is (all buffered): dash> c stick up > c stick up. The first c stick up initiates the dash attack so you can do it at the same time as the dash if you want, the 2nd c stick up is the one that's important though and the one you have to time based on the first c stick up. I think the best use for it is retreating SH fair > bdacus. Since the retreating SH fair is like a poke it leads into a strong aggressive bdacus and throws people off sometimes. I time it the bdacus right as Diddy pulls his legs back in from his fair. I don't really use it out of anything else since it's not that great from other moves like spotdodges or dtilts. Another good use is to use it out of an air dodge or as you're coming back on stage with a fair/air dodge. The best way to practice it is to just make sure you can do buffered dashs first, then buffered dash attacks and then practice bdacus.
You'll have to experiment with the timing yourself since it's hard to explain but the input is (all buffered): dash> c stick up > c stick up. The first c stick up initiates the dash attack so you can do it at the same time as the dash if you want, the 2nd c stick up is the one that's important though and the one you have to time based on the first c stick up. I think the best use for it is retreating SH fair > bdacus. Since the retreating SH fair is like a poke it leads into a strong aggressive bdacus and throws people off sometimes. I time it the bdacus right as Diddy pulls his legs back in from his fair. I don't really use it out of anything else since it's not that great from other moves like spotdodges or dtilts. Another good use is to use it out of an air dodge or as you're coming back on stage with a fair/air dodge. The best way to practice it is to just make sure you can do buffered dashs first, then buffered dash attacks and then practice bdacus.