Nearly every toy I buy I intend on opening (if not already loose). If I reeeeeally like it I'll have a second one to keep sealed. Out of 932 Transformers only 24 of mine are sealed.
In regards to how long I wait, I usually open things the same day I get them, or if it's one of those weeks where a lot of things come in I'll leave some for a bit, as it can be overwhelming.