Many times you'll never hear any response. Properties are being hit hard with multiple offers right now. The banks are usually only looking at the top 3 offers and disregard all others. Of those 3 top offers, they may hear the YES or NO. All the other offers many times get thrown on a pile and never get any attention what so ever. Usually the REO agents don't take the time to call or e-mail the 20 other offers that weren't strong enough.
If your offer is outstanding, it usually take 3-5 hours from the listing agent to confirm, and counter offer come over 2-3 days later. But sometime it really depend on the bank's decision. Just be patient, and it will finally come to you if your offer is one of the best!