Bringing people into a project late isn't a problem as long as you ensure that you provide them with work that is focused. The more focused it is, the less they will need to learn to get up to speed. Simply adding more programmers and expecting things to happen faster can do more harm than good!
Edit: as an example, the last startup I worked with hired 3 intern programmers to "speed things up", however as the most experienced developer in the team I bore the responsibility of managing them, and ended up not doing very much programming. Ultimately not a lot got done as they constantly had questions (understandably) and by the time they got up to speed in any given area the time saved was mitigated by my time lost. Unfortunately I wasn't part of the decision process that lead to that, or I'd have nipped it in the bud and hired a single other more experienced developer instead.