Plea agreements can take place at any time - I've even seen them reached while a jury is deliberating after the trial has been conducted. Your attorney can talk to the prosecutor and reach an agreement, but the final terms must be spelled out in a plea form that you have to sign and a judge will have to take your plea in open court.
Your attorney should be able to arrange for time for you to get your affairs in order before your surrender date. You may have to enter a Cruz waiver - meaning that if you don't show up to turn yourself in on the date and time agreed to, the plea stands but you can face up to the maximum instead of what you agreed upon.
Once the prosecutors have the case, it is possible for the defense attorney to negotiate with them. Typically pleas bargains are discussed on the day the case goes to court. Most courts are flexible in allowing you to surrender for jail on a later date. It depends on the type of case and your attorney's ability to negotiate for you.