The key to a successful bargain is timing. Here are some tips from the experts on how to save big in a few key categories.

HOTEL ROOMS

4 p.m. local time on a Sunday is the best time to book a room, says CBS News travel editor Peter Greenberg. Follow these steps:

• Call the hotel's direct line -- not the 800 number or reservations -- and ask to speak to the manager on duty.

• Tell the manager you're shopping for a great room rate and ask what the hotel can do for you.

AIR TRAVEL

The cheapest fares are usually at 2 p.m. on a Tuesday, says Rick Seaney of the website FareCompare. Most major airlines announce their sales on Monday nights, and this triggers other airlines to try to match those discounted prices on Tuesdays.

Tuesdays, Wednesdays and Saturdays are usually the cheapest days to fly, with the earliest flight in the day being the most cost effective followed by lunchtime or dinnertime.

GROCERIES

For markets, Wednesday is the start of the week, so that's the day you can get a discount on the previous week's goods, especially meat and poultry.

Stephanie Nelson, author of "The Coupon Mom's Guide to Cutting your Grocery Bills in Half," says not all stores follow the same schedule, so ask your local store when it does its markdowns, and you'll get great savings.

DINNER OUT

If you're looking to save on your restaurant bill, go out to dinner on Tuesday nights, when restaurants are least crowded, says Mark Di Vincenzo, author of "Buy Ketchup in May and Fly at Noon: A Guide to the Best Time to Buy This, Do That and Go There."

Large chains often will offer their best deals on Tuesdays, such as "kids eat free."

CARS

Go to car dealers in the early afternoon on the last Tuesday or Wednesday of the month for the best deal, because that's when they are interested in meeting their end-of-the-month sales quota.

The best time of year to buy a car is the fall, from September through December. You can expect to save 10 to 20 percent on the previous year's model. If you can hold out until December, your savings will be even bigger because it's the end of the year, says Phillip Reed, senior consumer advice editor of Edmunds.com.

RETURNS

The best time to return anything is 10 a.m. on any day, except Dec. 26. At that time, salespeople will be starting a new day ready to help their customers. And the most experienced salespeople tend to work the day shift, so you'll be dealing with someone who knows how to handle returns.