I'm presently doing about 10 programmers jobs, this is typical recession type fun. I have many clients asking me "When? When will you have my request completed?"
Considering the other requests that I have to fulfill it's a real balancing act. So how should I answer these clients questions, when the real answer is "When I get to you".
If you are using some kind of schedule to manage your work, you could see when it says the work will be done and tell them that.
If you are just running by the seat of your pants, you could try saying 2-3 weeks and see if you get away with it. Also, try and invest a little time into scheduling your work.
Have you estimated all the work that needs to be done to fulfill their request? Have you scheduled your time taking into account all the other tasks that must be done?
If you have, then the answer is simple: you tell them when you have estimated that you will have the work done, making sure that they understand that estimates are not deadlines.
Your clients should expect to have an idea when their projects will be completed so that they can schedule any work that relies on these projects results.
Get a better real answer. If a client is on a "when I have time" pile they should know that, and you should probably be charging them less, since they fill otherwise idle time. Otherwise, scheduling is your problem, not theirs. Estimation can be incredibly hard, but you have to make an attempt. Sit down with a calendar and block out days for each project. If one runs late then you can contact the owners of other projects and let them know that theirs will be delayed also.
Indeed it is, beyond question, at the appropriate juncture, in due course, in the fullness of time.
Truthfully -- that's how you should answer it. It's better to be dropped because you were too busy than for not delivering.
The next "couple" days you should have a general idea of what you'll get done. Get a feel for the actual priority of the request (it's always now to them but they may be able to get by for a little while longer) and prioritize days N and N+1 accordingly.