I would convert it back to Date with same format you've used to get this String. Any String manipulations will be fragile. You should hold your format String in one place, so whenever you change it, your code will still work as it should.
//Get this one provided by dependency injection for example
SimpleDateFormat sdf = new SimpleDateFormat("hh:mm a");
String dateString = sdf.format(new Date());
Date date = sdf.parse(dateString);
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
int hour = calendar.get(Calendar.HOUR_OF_DAY);
int minute = calendar.get(Calendar.MINUTE);