I was fortunate to pick up two expired domains that each have a few hundred incoming links to them for the keywords my primary domain is trying to rank for. I purchased them, and have now 301 redirected them to my primary domain. About how long will it take for Google to recognize these incoming links to my primary domain and impact the SERPs?
It depends upon a lot of factors such as PR, the nature of site, amount of quality backlinks, age of site etc.
I realize the size of the impact that they have will depend on all those factors. However, question is more around how long before any impact is realized? A day, week, month?