Depends on their skill level, whether they've done any competitive shooting/gun handling before, etc. Folks come to IDPA with different experience and gun-handling skills.
You ARE talking about time AND score (with points down for misses, bad shots, etc.), right?
If you're a raw newby -- 60 to 90 seconds is probably good, but I've seen folks do it in 150 seconds (and 450, overall.)
Someone reasonably proficient might do it in 20-30 seconds... A "master"-leve shooter in less than 20 seconds, on a good day. (Stage 1 is the easiest to shoot well, and the fastest for nearly everyone.)
(Most of us don't do it a stage at a time, but only as a 3-stage exercise; you've got to do it that way when you actually classify -- all the same day, without repeats if you do poorly on any one stage. It must be cut from whole cloth, so to speak...)