People get married all the time. Most people get married while working 40+ hours per week. You aren't going to prison, you are going to grad school! You might have to plan the date around your school schedule/breaks (and might need to start the program to get a better idea of when those times are), but really, if you are ready to get married, plan it! If you wait til you are out of school, when are you going to plan your wedding? During your first year at a new job when you don't have vacation days yet? You know what I mean? Unless you are independently wealthy, you aren't ever going to have a time in your life where you can devote any kind of majority of your time to planning your wedding.
Congrats on your engagement!