Should I add my index after the table is populated or before (MySQL. Aurora)

I know this has been asked in the past, but sometimes things change over time and I wanted to double check. I have a table with about 9 Billion rows. Should I add the index before inserting the data or after. I'm using Aurora. Does it matter if I'm adding more than one index? Everything, I'm aware of says you should do this after the insert, but one of my colleagues is insisting it's faster to do it on the insert.