I don’t think “three month limit” makes sense. The increase is an amount of money. There is no compulsion to spend any of it. A decision to spend more than it has is a decision that stands separately.
Classic propaganda. Rather than say they increased it $400 billion or whatever it is we overspend in 3 months, they phrase it so the public won’t freak out by the huge number. So we get “3 month increase”. That’s a lot more palatable according to the reactions from the test subjects polled.