My first tip would be: choose another airline. But, If you choose to fly with Buddha Air then be prepared for major delays. On all three of our flights with this airline we have had delays and got to our destinations much later than expected. The delays have lasted for more than an hour and none of the flights have taken off at the scheduled time.
The worst thing is that the delay from Bharatpur Airport to Kathmandu on 5th April 2018 resulted in our missing of an international flight on Jet Airways outward to Delhi, which meant a whole lot of extra cost, reorganizing flights and unnecessary mental stress.
Other airlines like Yeti Airlines were much more efficient, taking off on time.
Save yourself some mental stress and take another airline instead. And make sure you get travel insurance!