First and foremost your boyfriend should be talking to his lawyer, that is why he hired him. The length of probation is generally a pretty simple question and I suspect that the probation will end two years from when it started. In other words it will not wait to begin. Terms about things like guns can be more problematic. The judge often given discretion to the probation office, however this is something he needs to discuss with his lawyer.
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I totally agree that your bf needs to be talking to his lawyer. That being said, certain terms of probation are often negotiated by a defense attorney working with a prosecutor, the judge, and sometimes probation. Good luck.