I'd agree with the other posters. Hold off on asking for a time-frame right away unless you have something that requires bringing it up, eg. another job offer you are considering accepting.
I recently had that type of situation. I was laid off and looking for work. I ended up with two interview processes going forward at around the same time. It was around the holidays so one told me they were going to be off for the week between Christmas and New Years and they'd be moving forward with the process after New Years. The other was able to schedule an interview during the week between Christmas and New Years. I had the first interview and felt like it went well and they told me I'd hear something from them the middle of the next week.
When the other company got back to be after New Years to schedule an interview I let them know I was still interested but that I had interviewed with the another company and was expecting to hear back from them by the middle of the week. I ended up having a phone interview on Wednesday morning which again I felt went well. On the phone interview I let them know that I was still expecting to hear back from the other company soon about the other position.
I got that call shortly after the interview was done and was offered the job. That job offer was at a substantially better pay than I had been making and high enough that I was pretty sure the second company wouldn't have been able to match it so I accepted the offer. I called back the second company and let them know that I was offered the other position and accepted it and told them why. If I had thought the offers would have been closer I would have tried to get some time to make my decision to give the second company a chance to make an offer. In the end the I found out when I called the second company back that they were getting ready to move forward to an onsite interview, their last step, and the manager told me to let him know if I was looking for a job again.
A couple of general tips.
1) Follow their lead on communications. This covers all aspects of communications. Are they emailing you or calling you primarily? Are they being formal or more casual? Are they responding immediately or waiting a little bit to respond? Having been on the interviewing side of things I'd give people at least a couple days before you start asking about a time-frame as they are probably interviewing a couple candidates over a day or two and then need to work through their processes and determine if they want to proceed forward with any of the candidates or continue looking. If you want, it is fine to be slightly more formal than they are but you don't want to be more casual.
2)Be patient. True or not if you seem too eager it can make you appear desperate and people rarely want someone who "NEEDS" a job right now. If you "need" a job odds are you are likely you won't stick around as long as someone who is isn't desperate because you are willing to overlook, at least temporarily, a lot of things just to get that job you need but after a while those things you overlooked start to bug you and you will start looking for something else. I remember one candidate we interviewed for a position that we didn't move forward on because he didn't seem interested in the job. He wanted to move to the city and made it seem like any job in the city would do. In another situation I had a pre-interview and then waited a month and a half before they got back to me to finish the interview process.