Ordering for a Company

I was asked by a friend of mine who is the general manager of a company to start ordering their industrial products. The lady who use to do this is out on maternity leave. They basically need someone to fill in for a couple of months. He thought of me since I use to do this years ago for another company. Of course, I said yes, even though I really don't have the time. I know if I was in a situation and needed help then he would do the same for me, so how could I say no.