The treatment you are pursuing is an orthodontic treatment,  in some cases,  removal of premolars are very common to create space for correction of crowding of the teeth. The time duration is obviously around 8 months to 1.5-2 years depending upon the case,  once the braces r removed,  you have to wear retainers to keep the moved teeth in place.  Duration of wearing retainer also depends upon the case. For the proper knowledge of that,  you should ask it your dentist who is giving treatment.  He can very well explain about the wearing time duration of retainer in your case. Relapsing depends upon the efficiency n knowledge of the orthodontist from whom you are taking treatment,  your Oral hygiene status,  perio condition ( condition of your gums n bone holding the teeth) ,  Nutritional conditions of your body and upon the instructions given to you by your dentist. 

hi frd , steel braces are good , depending up on situation if space in jaw is less than the tooth material then extraction of premolar is most common, this is ortho treatment  , which takes time and after treatment you have to wear retainer for at least 6month to 1 year and yes some times relapse  does happen depending upon ability and efficiency of your dentist, if you don't find  my answer irreverent please ask me again