how often or how long after someone starts recovery do you think they relapse? i have heard it can be days to years where someone could relapse. does anyone know anything else about this? is it something that triggers them like stress or seeing someone else do what they were addicted to?

There's a number of reasons why a person could relapse.  That's why it's so important to stay in rehab until you're able to say no to drugs/alcohol.  And also the people you're around has a lot to do with when you relapse. 

relapse can happen at any time for any reason. Sometimes people relapse just by thinkiong they can control themselves. Like drinkers, some think that since they're sober they can manage how mcuh they drink, they can go back to just one cup. But that one cup is relapsing and most of the time their addiction starts again.

I imagine people to be most prone to relapse during the period right after they get out of recovery. They're back into the real world, they can get the drug if they want and they will for sure encounter things that remind them of their drug of choice.

I think people should have a plan for change as soon as they get out of rehab. They cant hang out with their friends that were on drugs, they cant be around places where they did drugs. I think having someone with them for a while is a very good idea also. A person needs to be most careful around that time because being back out in the real world and the easy access to drugs makes it a lot harder to stick to our words and whats better for us and just stay away from it all.