Anything from a month to never...
Make sure it is well optimised. Keywords are not important any longer (Google and Yahoo do NOT look for these!). SEs look for CONTENTS, "variablity" (a site in which the contents changes regularly), and "links to" (the number OTHER sites that link to YOU).
No need for you to link to another 100 sites does not count!
Re-submit your site every month as well.