I'll try to answer your questions. Maybe others will chime in, too...
Q: If you have a LIVE and SILENT auction in one event, when do you end the silent auction bidding?
A: We close our silent bid sheets in 2 or 3 different groups, and don't start our Live until after all the silent bid sheets are closed. During the Live, we prepare for cash out so we are ready when the Live auction closes.
Q: Do you always have food as something to do during silent auction time?
A: I think some (big?) auctions go as far as a sit down dinner. For our events, we've had strolling hors d'ouvres and a few food stations. It's important to keep people circulating through the bid sheets so we keep the food in the same room as the auction items. We've had both stand-up tables with an area of chairs for Live auction partcipants, and sit down round tables that could be used all night. Just keep people close to the action.
Q: Is afternoon or evening the best time to hold an auction?
A: That depends on your audience and what kind of event you want to hold. If you have it in the afternoon as part of a family event, the kids will be distracting mom & dad from the bid sheets. I know others have included silent auction items as only one component of a family night, but I wonder if their proceeds would be higher if the auction were the focal point of the evening. If you have an adults-only evening event, you can make it a very nice night out. Being dressed up (and, yes, having a glass of wine or two), makes the evening feel special, and the purse strings loosen.
Q: During the live auction, how do you log winning bids, item, and bidder number?
A: I'm sure there are other ways, and we've never used a professional auctioneer who can probably give you better advice, but....we have a special type of bid sheet for each of our live auction items. We put them in a folder for our auctioneer. As each live item is won, the auctioneer, or a runner, marks the winning bid# and amount on that item's bid sheet. The sheet is then run to our check out area where it is matched with any other bid sheets won for that bidder.
Someone else on this forum suggested hiring a professional auctioneer. I agree, even though our group has never done it. It's hard to watch an amateur try to read the auction audience. A pro knows how to keep things moving and how to get the most out of your guests.
Take some time browsing through this discussion forum. You can search for postings on auctions. I know there's more info out there.