It depends on the link. Some backlinks can get indexed in minutes, some take days, and some never get indexed.
Ok, and I heard that the better the link is, the faster it gets indexed, is that true?
Yes. If you are building links on quality sites, they should be indexed very fast.
If you are using automation or building low quality links, it can take a long time to get indexed (if it gets indexed at all).
Are you telling me that some of the package sold on these forum have actually a very small chance of helping my site rank higher?