Hello. For your questions concerning award payment, the latest NSF Phase I terms and conditions (https://www.nsf.gov/awards/managing/sbirsttr_conditions.jsp) states: “In the absence of an approved modification to this schedule, payments will be made by NSF as follows: The initial drawdown, for all but $25,000 of the grant amount, can be made after the period of performance start date of the grant. The final $25,000 will be made available upon approval by NSF of a satisfactory final report and upon submission of a Project Outcomes Report, as described in Article Project Reporting Requirements and/or in the SBIR/STTR Program Solicitation.”
So, if your proposal is awarded you will likely receive the majority of the funding soon after the project period start date. To get specifics concerning your award information, I highly recommend meeting with your Program Officer (PO) soon after you receive a notice of award.
Also, completing the project early should not be a problem as long as you provide the final project report at the end of the proposed project period. Again, the best thing to do is confirm NSF expectations with your PO.