Because Lantus is a depot insulin, shooting early does act like a dose increase. If you have to shoot one hour early, depending upon the pre shot test number, maybe you could give a slightly reduced dose that cycle. I don't think I'd advise shooting 2 hours early and then leaving the house, as that could really affect the depot and act like a dose increase. If you're only going to be gone in a couple of hours, I guess you could manage, as long as you would be home to test the rest of the day, but if not, I would advise against it.
Do you have a spreadsheet set up?