CVS test won’t work because it is rapid test. And the airport rapid test is costly. One of my friend paid $400 at the airport. Airport rapid test still takes 4 hours if you want to do it at airport.
For nepal they require rt-pcr. Let’s say If you flying on Saturday at 1 pm. You can take your test anytime on Wednesday. If the turn around time for test is 48 hours you can get it on Thursday as well. It depends on the lab for turn around time. Most of the state sponsored clinic do it for free. I did my test for both Wednesday and Thursday to be on safe side for my Saturday morning flight.