You receive an offer: Look at the offer. It's that simple. If you want to wait for the second offer before deciding, that's OK. It's your decision. But what's this nonsense about not opening it until a second offer comes in? That's assinine.
After all, that second offer may never come in. Or that first offer may require you to accept or counter within, say, 24 hours. Never, never fail to open an offer because another offer is expected.
As for your Realtor's advice. Huh? First, you're the boss. The Realtor is just your agent. You can do whatever you want, though--as I noted above--the way it should be done is to look at the first offer immediately.
And you don't have to take orders from the broker, either.
What I suspect happened--and I'm only guessing here--is that your agent (for some odd reason) told you to wait. He reported this to his broker who said, essentially, "You idiot!" So your agent called you again and reported what his broker was trying to say (and what I'm saying): You open an offer when you get it.
As Patrick notes, if the first offer provides enough time, you can wait until you receive the second offer before deciding which to respond to, and in what manner.
Hope that helps.
If I were advising my client, I would wait to reply until the other offer is received so long as there is no indication that we could lose the first offer by waiting an extra day.
Not sure what you mean when you say "open" the offer. Reviewing it will not obligate you to accept or deny the offer. The duty of your agent is to deliver all offers to you in a timely manner but he/she can not tell you what you must do with it.
Neither does his Broker.
The only dictating might be done by the OFFER itself, which might include a very quick response time: The Buyer have the right to demand a 24 hour answer. You are free to ignore it, at your jeopardy; but they can demand it.
If I had an offer in my hand, I would look at it; irrespective of 12 offers coming tomorrow.