You're doing it wrong. If you're having that much trouble with deadlines and bandwidth, you should be inspiring your CEO, board, and investors to solve that problem. You should also make sure that you're providing them with honest estimates and not over-promising what your team can achieve.
Even if they do it willingly, pressing so hard on your team is going to lead to burnout and turnover in the long term, and lower quality deliverables in the medium term. Those almost certainly cost your startup more than a postponed feature or missed deadline.