Have you checked what it would cost to change the positioning flight to a day earlier? It might be minimal, plus presumably a night in an airport hotel, which could be worthwhile versus worrying and possibly losing a big international flight that you want to take. It sounds like you have separate tickets, and unless it's DL to DL, I wouldn't expect much help in rebooking if things go wrong on the day of travel. If you wait too long, your options could be more limited and more expensive. How risk averse are you?