You should allow yourself a couple of months to write the plan, even if it's only a few pages long. Developing the plan is the "heavy lifting" of marketing. While executing the plan has its challenges, deciding what to do and how to do it is marketing's greatest challenge. Most marketing plans kick off with the first of the year or with the opening of your fiscal year if it's different.
Rallying point: Your marketing plan gives your troops something to rally behind. You want them to feel confident that the captain of the vessel has the charts in order, knows how to run the ship, and has a port of destination in mind. Companies often undervalue the impact of a "marketing plan" on their own people, who want to feel part of a team engaged in an exciting and complicated joint endeavor. If you want your employees to feel committed to your company, it's important to share with them your vision of where the company is headed in the years to come. People don't always understand financial projections, but they can get excited about a well-written and well-thought-out marketing plan. You should consider releasing your marketing plan--perhaps in an abridged version--companywide. Do it with some fanfare and generate some excitement for the adventures to come. Your workers will appreciate being involved.