It would be best to put some extra days to return back to Kathmandu, if you don’t have enough time, then on the list put one extra day. Normally everything will go smoothly if in case your flight is delayed (Lukla to KTM) due to not favorable weather. These extra days will recover you to go to your further destination. The high mountain weather is unpredictable, it could be changed at any time. The reserve days will be covered to catch your normal schedule.