no one really knows. even the update that took place at the of april took place later than expected generally 2-3 months....but as mentioned no one really knows
The average seems to be around 3 months but like sadhivm said no one really knows. It is best to just focus on improving your websites.
How can you be so sure? What if Google decides "screw it" and doesn't update until next year...that would sure throw a couple people off