It really doesn't matter when you want to ask her. By asking her now, it would probably make her feel more secure about the relationship during the one year apart from you. Or if you're not sure about her commitment to the relationship, wait until you get back to see if she is faithful to you. Either way, if it's meant to be, things will work out. Just make sure she is the right one and both of you are commited to God and put God first in your hearts. As you can read with all the marital issues discussed in this forum, it's better to have a spiritually mature relationship before getting married.
Good luck and may God keep you safe abroad.