Hi
Create a New folder say, on the desktop. Backup your project to this folder in case of problems.
With your three sequences on the timeline making up your 45 minute video move the cursor to your selected division point and split the timeline.
"Save project as"
Delete everything to the RIGHT of the split position.
Close the gap and export what remains on the timeline. This will be your first video.
Reload your saved project from the .vpj file you "Saved as".
Delete everything to the LEFT of the split and export what remains on the timeline. This will be your second video.
Nat