It sounds like you're trying to guarantee that you will be waiting before the other person. This is usually fruitless, since aside from anything else planes can land early. It's also kind of unfair, unless your time is clearly less valuable than theirs (e.g. because you're picking up an important client, or because you know the traveller will be exhausted and desperate to get home as quickly as possible).
I would ask the traveller to estimate. Unless they're relatively inexperienced, they have as good a notion as you do that it takes a while. They have more idea than you do what their baggage, customs and immigration situation is. And most importantly, if they tell you that they expect it to take at least X minutes, then they've given you "permission" not to be there if they're any earlier. They won't be all that disappointed when you aren't, and you won't feel bad.
Arrange a back-up meeting place to wait in the event that you're not standing at arrivals.
My rule of thumb when I'm guessing what bus/train I can catch away from the airport, is that it's not worth even looking at less than 30 minutes if I have checked baggage. Most commonly I perform this calculation for Heathrow or Gatwick, which admittedly are not the smallest or fastest airports in the world.
Still, you can probably add that 30 minutes and be reasonably safe. They're unlikely to do better than 20 minutes for anything other than "trivial" cases (Schengen/domestic, no baggage, normal-sized airport as opposed to say Schipol which is vast and has correspondingly long taxi times). They're unlikely to be massively inconvenienced by waiting 10 minutes, provided they know you're on your way.
At large airports you can probably add an hour and still be there first half the time or better. Just pay attention in future to when you arrive and how long you wait.