Though you may not have enough time or resources right now to finish, you have some time available to get started. Every book that was ever written, no matter how lengthy, was written one word at a time. Every race that was ever won was completed one step at a time.
Great accomplishments come from stringing one effort on top of another.
With enough small efforts, anything can be achieved. Though you may not have the time or the resources to make a big impact, use what you do have to make a small difference. Do it often enough, with commitment and focus, and the big results will surely come. Don't waste the time you have by complaining that there's not enough of it. Use it to do what you can.