Problem with time zone conversion iPhone

Question

Dear All,

I have a date in milli seconds(EST) and a user specific time zone. I want to convert it to the user specified time zone. Following is the code I tried. Need help:

 float val = ([managedObject.lmt_ms floatValue])/(1000.0);
 NSDate * dt = [NSDate dateWithTimeIntervalSince1970:val];
 NSTimeZone* sourceTimeZone = [NSTimeZone timeZoneWithAbbreviation:@"PST"];
 NSTimeZone* destinationTimeZone = [NSTimeZone timeZoneWithAbbreviation:usrtimezone];

 NSInteger sourceGMTOffset = [sourceTimeZone secondsFromGMTForDate:dt];
 NSInteger destinationGMTOffset = [destinationTimeZone secondsFromGMTForDate:dt];
 NSTimeInterval interval = destinationGMTOffset - sourceGMTOffset;

 NSDate* destinationDate = [[[NSDate alloc] initWithTimeInterval:interval sinceDate:dt] autorelease];
 NSLog(@"Dest time is:%@",destinationDate);