Many businesses are like that. For a car salesman, when will the next customer walk in the door?
On the OP's question, it's a good feature, but the question is, how would we word it so people don't expect to get something after that specific amount of time? "it said 7 days and I waited more than a week and didn't get anything!" Approx, average, but still they're going to think that way. It can't be a whole sentence, unless we think of somewhere else to put it, but where would that be? Suggestions?
The difficulty quadrupled a few minutes ago to 181.54. It's going to take typically about a week to generate now.