Well, an average skilled Dominix makes like 15m isk/tick baseline (more with better skills).
15m x 3 ticks per hour = 45m isk per hour x 10 hours = 450m isk for a krabbing character in a 10 hour period.
So you could have 1 character krabbing a system for over 10 hours to get close to that, or 2 characters krabbing for 5 hours, 5 characters krabbing for 2 hours, etc. etc.
I don’t know if there’s any greater effect if you krab beyond ~500m isk per 25 hours. Someone on r/eve did the calculations and found that was the first threshold where your DBS percentages will drop. I’m sure someone else is doing more testing to see if, for example, krabbing 1B isk in 25 hours makes your DBS drop more or something. But I haven’t seen anyone posting the numbers yet, so I’m not sure how that works.