1 month should sufficeNot exactly. It’s one thing to say, “I’m outta here.” But it’s another thing to say, but I can’t do this job for any other company in the same line of business with “X” miles of the office and/or for “Y” number of months.
In that latter case, sure they can leave. BUT, how they will get a new job is very complicated.
This is why our courts generally put a limit of reasonableness on the time and the scope of any “noncompete” clause.