You can fill up the visa application online before you depart to Nepal. You can also call Nabil bank in Maharajgunj where you can ask them the trend of Interview Dates given after Paying for Interview Fee. Once you file application online, you can ask your friends or relatives to pay the Fee at Nabil bank and book your interview date. You can arrange your Interview date the day after you land KTM. If PIMS require, it might take 3/4 additional days otherwise you are straight.
Good Luck, BTW I am also going in April n again Stamping, It's fun LOL. The above was my experience on April 2014. I appear in the interview 2 days after I landed.