As a PhD student, is it worth spending time organizing a contest for a conference? I am a PhD student in computer science: is it worth spending time organizing a contest for a conference (e.g. a shared task for a conference in natural language processing)? I think that would be a great experience to have, and fits very well my research interests, but I am afraid it might slow down my research and therefore delay my graduation date.
Often in graduate school there are an abundance of neat opportunities and experiences; it can be difficult to decide which tasks to pursue. You'll need to consider the short and long-term career benefits of organizing the conference, as well as how it will be viewed within your program. In regards to short term career development, this may be an opportunity to provide an academic service activity for the conference, though there are often less labor-intensive ways to add that type of experience to your CV. However, if you're interested in a career in management or administration and want to gain experience in developing or implementing organizational activities, this might be a valuable long-term experience. Also, if the group task will result in data that you can later use for publications or products, it may be worth the investment; it may even serve as a unique research opportunity. 

Whether you pursue this activity will likely also depend on whether your mentor is supportive. If you are concerned that this might delay your research and your graduation date, you will need to decide not only if you can live with pushing back graduation, but if your mentor or program will support that as well. If you are able to pitch this opportunity in terms of career development benefits, products, or even positive publicity your mentor or program may be supportive. They may even provide you with some undergraduate assistance to reduce the burden of coordinating the event. Before you have that discussion, make sure you have a clear picture of the pros and cons, as well as what (minimal) supports would allow you to take advantage of the opportunity at the lowest possible economic, time, and labor costs.