Fabi, not many people succeed in langauge exchange (because most people are English learners and it is hard to find partners for them:)) and there is no established routine.
Be avare about one problem: some people are just unable to follow any schedule. I mean, to schedule a session in 17:25 and actually be there in 17:24. For others it is impossible not to follow it. And both group expect you to be like them. Any agreement with people form the first group is approxiamate:) A cancelation would really destroy mood of someone from the second group.
Of course people from both groups could try to adapt to each other, but it is not easy. What people from the first group can't understand is that people from the second group actually live like this: 15:00 they drive from work to home 16:00 take kids form kindergarten, 18:00... and so on. What people from the second group don't understand about people from the first group is that scheduling things can also be a torment for them.
Just be prepared that when someone is saying "yes, 15:00" (1st group), then she may not be able to be there at time, and when someone says "no problem, let's do that a hour later" it can be a REAL problem for her, she just canceled something to have a free hour for you and you didn't come.
What works with people from the first groop is just "are you awailable now?"