You should be able to start a return as soon as the tracking shows that delivery has taken place. It may take a while for the system to catch up.
Be sure to use the reason "Not as described". If you use "Doesn't fit" that is classed as change of mind (buyer's fault) which sellers can refuse.
eBay instruct overseas sellers to cover cost of return postage but they cannot enforce it.
It might be simpler if you resell them yourself when you get back.
