Since Google algorithm changes very often, there is actually no guarantee of instant or quick improvement of result. Different businesses have different target market, different competition & different needs. Link building is a continuous process and it 100% helps in gradual improvement of site's ranking. The time frame can be 3 months, 6 months or 1 year. It's  an important part of SEO, but it's not the only part to affect a site's visibility or ranking. There are various other tasks & pointers to be covered to get better visibility. Proper link building & content marketing strategy should be implemented depending on the website's analysis & requirement. Also you have to take care of other important things for SEO (On-page SEO, content, design, updates, internal link structure, Local/Social profiles etc)