Vienna is 4.75 hours behind Kathmandu
Best overlap: 12:45 PM to 6:45 PM in Kathmandu is 8:00 AM to 2:00 PM in Vienna.
12:45 PM to 6:45 PM in Kathmandu is when Vienna is also working, at 8:00 AM to 2:00 PM their time. The 4.75-hour gap barely gets in the way — you've got 6 hours of overlap, so pick whatever time fits the agenda. Just remember Vienna changes its clocks for daylight saving and Kathmandu doesn't, so confirm the overlap whenever the seasons turn.