Depends if the site is old or not, how many pages on the site, what keywords you are going for. I would love to know what the algo is for this. Any google employee is welcome to sticky me with the answer :)
When Should I Slow Down Acquiring Links so that it Looks Natural?
Why slow down? If yor are getting links, keep getting them.
It is quite possible the most popular site on the internet two years from now does not even exist today. Certainly, in a couple of years there will be several new major sites that do not exist today. For a site that goes to the top of its SERPs, what will their linking history look like two years from now? We would most likely see that the site started out geting links immediately and that the rate of link acquisition increased steadily over time. There would likely be no slowing down.