If your boss or a customer asks you to do something, do you always instantly say yes? If you fail to get the job done in time or it turns out to be impossible to do, you end up looking bad. Instead, mention that the job sounds like it will be an exciting challenge and then take a few minutes to gather the details. Don’t be afraid that asking questions will make you seem incompetent. Getting the job details wrong looks much worse.
Once you know what is involved, you will know whether it is possible to deliver the job on time or if you will need to say you’d love to do it, but will need additional time. Then, do your best to do a better than expected job and get it done on time.