USCIS policy is to designate TPS for 6 months/a year/ 18 months.. Nepal was designated for 18 months . If the condition do not improve back home they will extend again.. Research Haiti and Honduras TPS details in justice dept web site to get an idea..
Fyi.. U can still apply Tps on late filing but you will have to satisfy one more additional condition .. Check USCIS website for TPS late filing....