How long do you have to wait inbetween BBL rounds?

I would recommend waiting at least 6 months in between liposuction and BBL rounds.  By 6 months, the swelling subsides, final results are achieved, and re-evaluation can be done. Seek a plastic surgeon who performs hundreds of these procedures, has great reviews and photos, and is an expert in this field.

I would want to gauge what your permanent result would be from the first transfer.  Swelling with fat transfer can persist for significant amounts of time.