Most successful academic grant proposals are the results of month of planning and preparation, so you will want to plan ahead to give yourself adequate time. It is important to think about how your proposed project fits into your longer-term professional plans, and in many cases, there are several building blocks that contribute to the creation of a successful grant application. Possibilities include: securing references; incorporating feedback from your colleagues/experts in your field; collecting data; seeding your project with a smaller grant; and familiarizing yourself with online submission processes; etc.
Last but not least, planning ahead allows you to craft a much more competitive proposal, because you've had the chance to work out any problems or idiosyncracies.
Special note: When you are working toward a specific grant opportunity deadline, you should plan to formalize your plans with the C&F Office at least eight weeks in advance of your proposal deadline.