It's hard to know. Maybe somebody else knows, but why this is important? The more links your site has the sooner will google visit you.
use your google webmaster tools, awstats or G analytics or whichever you use to see when the spider was there last.
not sure exactly, I use stat counter but I will look at analytics real quick and see if I can find it.
If you're using google webmaster tools, then you can know the Google's last bot/visit by logging into the GWT. If you're not starting using it, do it now.