src/main/java/com/groupon/uuid/UUID.java
public Date getTimestamp() {
        if (getVersion() != VERSION)
            return null;

        long time;
        time  = ((long)content[10] & 0xFF) << 40;
        time |= ((long)content[11] & 0xFF) << 32;
        time |= ((long)content[12] & 0xFF) << 24;
        time |= ((long)content[13] & 0xFF) << 16;
        time |= ((long)content[14] & 0xFF) << 8;
        time |= ((long)content[15] & 0xFF);
        return new Date(time);
    }
public Date getTimestamp() {
        if (getVersion() != VERSION)
            return null;

        long time;
        time  = ((long)content[10] & 0xFF) << 40;
        time |= ((long)content[11] & 0xFF) << 32;
        time |= ((long)content[12] & 0xFF) << 24;
        time |= ((long)content[13] & 0xFF) << 16;
        time |= ((long)content[14] & 0xFF) << 8;
        time |= ((long)content[15] & 0xFF);
        return new Date(time);
    }
Extract timestamp from raw UUID bytes and return as int. If the UUID is not the default type, then we can't parse
the timestamp out and null is returned.
@return Millisecond UTC timestamp from generation of the UUID, or null for unrecognized format.