I have a Fisher & Paykel Aqua Smart. It's a top loader, but designed as a front loader. It has a function for nappy washes, so does a rinse first, then a gentle wash. I've never had any issues with it not washing effectively. Washing time, I'm not sure actually as I've never timed it. I'll report back next time I do a nappy load The Aqua Smart is a water saving machine (as it's designed as a front loader).
i have this too and love it! we've never had any problems with cleaning the nappies. think it takes about an hour from memory (just under maybe)