Baltimore is a pretty big area, so where in Baltimore? Car or public transit? Presuming usual rush hours (something like a 9-5 M-F job)?

Without further info, I'd say 1 hour is the minimum under ideal conditions (not likely to occur often), 2 hours on a bad day (but not worse case--figure 3 hours if driving and a major accident occurs on I-95), so maybe 1.5 hours on average each way or 3 hours total per day for commuting.

For the record, I know of nobody who lives in DC and commutes to Baltimore, though I'm sure that a few people do it. I know a number of people who live out that way (whether Baltimore, Annapolis, or small towns out there) and commute into D.C.