CXX-321 remove optime

I think you can use ConstDataCursor here to make this a little more elegant:

ConstDataCursor cursor(value());
const uint32_t increment = cursor.readLEAndAdvance<uint32_t>();
const uint32_t seconds = cursor.readLE<uint32_t>();

That removes the magic constant '4'.

If you don't want to use cursor, then re-write this to use sizeof(uint32_t) rather than '4'.