Hi!
It's simple! Just charge!
Discharging is an option but is not necessary! I have the same charger as you, but use it mostly for charging my A123 packs.
NiMH cells (or NiCad cells) are better slow charged with a 50-150mAh wallcharger.
But why use old NiCad cells on just 600mAh when there is NiMH cells available , the same size and weight, at 2000-2800mAh??
NiCad cells is no longer used over here in Europe! Why still in the US????