There are plenty of reasons why you might be considering moving, from just wanting to get a change of scene to moving into a bigger house to relocating so you can take a new job. Why they want to move can have a million different answers, but for most people, when they want to move is the big issue.
The first and most important way to answer this question in most cases is 'not right away.' Just because you just got a new job doesn't mean you should stuff everything in the van and speed across the country without taking a little time to relax. While you're relaxing thinking about the move, it's probably also a good idea to look up grocery stores and gas stations around your new address.
If you have kids, don't be that mom or dad that makes the family move in the middle of the school year. Starting a new school right after a move is hard enough, and you don't want to just drop the kids in a foreign area without giving them time to make new friends at their own pace. If you don't have a choice and have to move before the school year's over, allow the kids a little time to get used to the area before throwing them headlong into a new school.
Moving on a weekend is also a bad idea. Moving places are extremely busy on weekends and won't be able to answer all of your questions if they're too busy. If you get to your new home and find that the water or power are still off, you'll have to wait until the next weekday to do anything about it.
The best time to move is different for everyone, but it has to be when you're ready for it and when you're feeling good about the move. Find some fun things to see and do as soon as you get to your new community, and do some exploring. Get excited about going and make sure that you feel good about the move before you pull out of your old driveway. Never move if you still have objections about it or you'll find that getting used to your new home is more painful than it should be. Even if you're not moving for the best reason, remember that it's an opportunity for a new start and make the best of it. Think positively. If your old house has depreciated and is falling apart around you, sure, that's not the best thing. But by thinking positiely you'll realize that you're moving into a better area and starting a better chapter in your life.
There is no specific best time for people to move across the country. The best time for you to move is when you feel right about what you're doing. If you're moving with your family, make sure everyone has a positive attitude about the move and that the time is convenient for them. The happier everyone is as they leave the driveway, the better your adjustment will be after the move.