Is there a best practice or any documentation that suggests when is the best day of the week and/or time to launch a Web site. Basically, what would be the optimal time to launch the site so it gets the most exposure/traffic? My boss/client wants to launch their redesigned Web site on a Sunday at 5AM in the morning. Seems like a ridiculous time to launch.
I think by Wednesday/Tuesday at the afternoon time of PST
Sonyk, if this is for a brand new website you are probably best launching it on a monday where people come back to work (so are more likely to be searching for your services), if you are launching a new service however it’s much easier as you can measure traffic logs for the busiest times of the day / night 
When your site gets the most traffic/exposure would depend on your target audience and the product/purpose of the site. Are people more likely to be accessing from work or home?
Since you mentioned redesign in your post I suggest you look at your site statistics.
By launch do you mean upload or promote?
If you mean upload, I don’t think you would want to launch the site at the time when it is busiest. Think about a physical store’s “Grand Opening.” These usually happen after a store has been open and operating for a week to a month. This gives time to work out any kinks. Then the big promotional event happens.
Sunday 5am sounds reasonable to me. There is almost always at least a small glitch to be taken care of. Best to take care of during an off time.
If you mean promote I don’t really think it matters unless you are having some limited time contest or something that coincides with the launch.
Monday 2rd September 2043 is the best day… 
Start of a week otherwise. But don’t send emails out before Tuesday lunchtime, people use Monday to “catch up” and are more happy with the delete button.
Time of day doesn’t matter because whatever time you pick it will be that time somewhere in the world.
Day of the week doesn’t matter either unless you have some sort of massive advanced advertising campaign that lets people know in advance that the site is due to appear on a specific day. If you do have such a campaign and therefore expect to receive a handful of visitors on day one then launching on a Monday for a site people are more likely to visit during the week or a Saturday if you expect most visitors on the weekend would be the best choice - probably at 12.01am New Zealand time so that it is there at the very start of the working week/weekend for all your potential visitors.
i dont really think it matters that much! an ebay listing its important but not an actual website. my 2cents
It should be launched whenever it’s ready, and you have the okay from your client/boss. There is no “optimal” time to launch since the web is always open 24/7/365.
In your case, unless your regular working hours fall within that 5AM on a Sunday, yeah, it’s a little rediculous.
Remember, with any launch there are likey to be a number of minor issues to work out, so a launch is never “open the doors and leave it”.
On another note, I agree with some of the above comments about sending out emails announcing the opening of the website…monday is probably a bad idea…tuesday or wednesday are probably better. The date and time of the site going live can still happen on monday if you so choose.
Your question is N/A (not applicable). Launching a website is not like mailing out a direct mail piece, where the day of the week matters. It doesn’t. The Internet is open 24 hours a day, 7 days a week. So anytime you choose to launch is fine.
David Jackson
Day of launch doesn’t really matter… because you’ll still be waiting for google to rank you.
If you’re talking about the launch of some sort of service, well, I’d suggest a tuesday or wednesday. Middle of the week, people aren’t as cranky
Well it would certainly give you some time for testing on the live server when most people are asleep.
I always giggle at people who worry about these things, like a website launches and miraculously gets an avalanche of traffic 2 minutes later.
The only time that happens is if you have a large marketing campaign or large joint venture partners for a limited signup site.
Any time is a good time. It’s the marketing that matters!
This is perfect advice on marketing emails! It’s so true!
Since the web is accessible from everywhere in the world there is never a time that more than about 1/3 of people are asleep and never a time when less than about 1/3 of people are asleep. Whatever time you choose, about the same number of people will be awake.
Whenever you launch will cover a 25 or 26 hour spread in timedue to time zone differences. Depending on where you are Sunday at 5AM could also be as early as Saturday at 3AM or as late as Monday at 7AM at other places where people interested in your site may be located.