I'm a PhD student. A professor that I collaborate with (not from my university) asked me on two separate occasions to help with grants that were due in a week. In both cases I managed to squeeze out 20 hours to help him, and he paid me out of his own pocket (not using grant funds).
How can I tactfully ask the professor to bring requests to me earlier in the future? I guess one way is to simply decline future requests that I cannot handle. But I want to preserve goodwill when possible - I could quote him an insane hourly rate if he again approaches me at the last minute, but some people might view that as me taking advantage of the situation, even though it's not my fault that he approached me so late. (The rumor mill can always turn white into black.) The best solution, in my opinion, is to successfully persuade him to approach me early.