Once you have AGI you use it to collect resources to cripple competitors and to build a snowball effect to make yourself unbeatable. 3 months of AGI is enough in the right hands to dominate the world economically.
Only if the AGI is cheaper than a human, in the case the AGI is more expensive than a human there wont be any snowballing. And the most likely case is that the first AGI is more expensive to run than a human, a few months of having overly expensive human level AI bots wont disrupt the world at all.