I own one of these chargers.
If you have enough time to leave your battery pack charging, use the .9A setting. The slower charge rate will be better for the battery and result in a longer-lasting charge. That being said, 1.8A of current probably isn't going to do any damage. Especially since Intellect cells are quite good.
You dont really have to discahrge a NIMH, although it is good habit these batteries dont have memory effects
Depending on the quality of manufacture, NIMH can develop a sort of temporary memory. While it is not critical to cycle (charge and discharge) the cells on a regular basis, it's best to avoid leaving your batteries charged for long periods of time.