When more than one task must be completed, it is always better to do one before the other. I discussed that earlier in the post Parallel processing in a project team.
An individual customer with a new question could think that it is even quicker if you fit his project in between. We have to make them aware that if we allow interruptions of any kind in an agile sprint, nothing will ever be completely done. What can we tell them? There will be other people with new requests while we are working on your task.... should we honor their requests to interrupt our work too?
They should understand: agile sprints are not interrupted. They are either completed, or canceled.
Image from Flickr by brittgow