To your first question: results are starting to come in, but the exact time depends on your NSF topic and the scheduled date of the review session hosted by the NSF Program Director overseeing your topic.
As to your second question, this is difficult to answer because of the large amount of variables. E.g. are the changes minor, or would they require some additional research to be completed? Can the proposal in its essence be resubmitted, or does it require a fundamental reorientation of the priorities? Regardless, with NSF moving to submission windows rather than hard submission dates, you can make sure your proposal is in optimal shape to be submitted, avoiding the need for a last-minute scramble to submit.
Let us know if you have any other questions!