Last time, when i returned from kathmandu, my visa was only valid for slightly more than a month.the inspector at the port of entry simply asked " you didnt renew your visa?" then i replied him" yes, i had only few days left to return for classes, and there was a long queue in US embassy of Nepal to have visa interview appointment, thats why". then he took it very easily and simply said "i see, thats okay" hope this helps