How long to keep redirects for seo juice

Hi,

This is related to what is the best policy for redirecting sites using 301 for link/domain juice.

Two or three months one of my sites reappeared in the natural search listings of Google after it plummeted out of natural search due to bad backlinks put in place by companies I hired to manage my SEO. I had run a disavow project end of 2013 and wasn’t expecting the site to eve reappear even though I didn't receive any warning from Google.

So, when I noticed the site reappear I decided to redirected one of my other sites to the destination site to give it a boost in Google natural search.

Both of my sites were dedicated to the same service. Very similar content and urls. They positioned slightly different in that one attracted keywords directly related to the services the business sold and the other towards the staff that I hire to get the work done. Otherwise the keywords, structure and target audience is the same.

I have two questions.

I redirected each page individually from the staff related site using a 301 in the htaccess to a similar or corresponding page on the destination site.

However, I didn't redirect the domain itself i.e. "/" file to the destination site until just recently.

What difference would it make doing it the two ways I already have?

How long do I need to keep the redirects in place before I can put the original site back online?

I’ve done that before. Used a site to redirect link/domain juice. Once it boosts the destination site in search results, I retrieve the old site by deleting the 301s.

Plus, what would you consider the best policy for redirecting sites using 301 for link/domain juice?

Thanks