Depends on your job. If you have a position at platoon or company level, you are probably OK for most of your weekends while in garrison. Once you get into battalion HQ, especially in jobs like Adjutant or Operations Officer, you can expect to work early, late or on weekends just to stay ahead. Once you move out of battalion to a Brigade or Area HQ, especially in a key job such as in the G3 shop, you can expect to come in on weekends when things are busy, especially if you are required to spend time away from your primary job by attending conferences, etc.
As Chags pointed out, if you are a Reservist or a Regular assigned to the Army Reserve, get used to working weekends as a regularly scheduled part of your life. Sometimes you may get only one weekend off in a month. The CTO day each week is programmed in to deal with that "shift schedule" for folks on full time service with the Res, but that day is not a guaranteed right and you can't always take it.
Cheers.