add it right away. Search engines will shove you into a 'sandbox' for a period of days..30 in the case of google, basically, your site wont feature at all, untill the spider bots have indexed most of your site, and then they only really rank you if you have activity, so once your done registering, make sure you post daily
I would say it is best to submit it straight away although freeforums forums don't seem to index well in search engines as this site always indexs in google with sid=123456789012345 or something on the end meaning everytime the bots visit the get a different session id so the index page for example has been indexed about 4 times. There is a mod to help this but freeforums don't have it.
After hearing that Google don't look for Meta tags I went a put it in my link in forums I visit across the web. I don't know whether it made any difference, but I did notice the site a bit more on Google (it wasn't the Noortie Fings one).
Like what has been said, just submit soon to get it indexed quickly. Then you can worry about getting people to improve your page rank in search engines.
What i would say is if you open your site immediately then submit your site there and then and posts lots so there is always new content for the bots to index. If you want to spend a week or something making it before you open then do not submit until you open then after you submit it keep posting so your forum has lots to index. Quite often bots find your site anyway as some of the bots have found this site before i submitted it. Although i still can believe that the MSN media bot has visited much more then the actual MSN bot here. -~-
The google bot here indexes alot of pages a day and is on most of the time. If there is not much to index they won't visit much.
I only started my new forum 5 days ago, and enabled the board about 2/3 days ago, and almost immediately had a google bot and yahoo bot visiting.
Now, I've notice, that they visit each time a new post is posted. google more frequently than yahoo though.
All be it that Yahoo bot had been bugging the Heck out of Noortie Fings since its early days, I was shocked the other day when I typed in Noortie Fings into Yahoo search to discover it was not there.
I had to submit it manually, then I popped across to MSN and did the same.
Yahoo takes much longer for your site to appear in. This site appeared in Google within the first day or so and is not yet in yahoo (well it wasn't yesterday) and 1 page is in Msn. I am now starting to get a few other bots visit here now like Alexa and the gigabot (whatever search engine he is from -lol- )
There is a reason behind the yahoo spiders causing loads online at one time but i can't remember but i think it was something to do with the way they index sites.
I'm not sure how my forum stands as far as bots, I started it about 2 weeks ago. I have to admit, I have been neglected it much since than and focusing on my main site and photo gallery (which a lot of bots frequent). When I promote, its almost singlehandedly just the main site and not the subsites. Is this a bad thing?
I would suggest getting a Google Account and using webmaster tools. Thats what I do. It won't show the "sid=54544454545445645" or whatever. You can set it to what you want the name to be on Google. Like http://www.forumpromotion.net or forumpromotion.net. I think there was a couple more options but I can't recall them at the moment.
Sumbit as soon as your site is live and functional. Let the search engines watch your site 'grow-up'. As your content grows, you'll see more organic traffic.