Thanks for correcting me.
On March 3, I will leave at work at 11:15 am to take my sun to the doctor. I will let you know the total amount of time that I would be taking ( how long I will be out of office) for this appointment once I am return to work.
On March (do you mean May?) 3, I must leave the office at 11:15 to take my son to a medical appointment. I'm not certain how long the appointment will take, so I cannot tell you what time I will return, but will let you know the total number of hours once I am back in the office.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.