It's still a bit of a haul from the entrance to the Palazzo to get back to the sands expo. You have to go through Palazzo, then through part of the mall between Palazzo and Venetian before you get to Sands.
The conference center is in between the Venetian and Palazzo parts of the resort. On the casino level, it's behind where the Delmonico's and AquaKnox restaurants are. On the shopping level, it's behind St. Mark's square. So add a few minutes from actually walking into the Palazzo.
And it's a
huge facility, so could be another 5-10 minutes to the actual conference room/ballroom.
Walking anywhere in Vegas always seems to take longer than you think. I would say 20 minutes to the conference center from Wynn, and 25 from Encore. Of course even if you were staying at the Venetian/Palazzo it would take you 10-15 minutes from your room.