[PvK]

You can definitely plan for different groups to move and attack at different times by varying the orders as you suggest. Managing my armies' tactical arrangements and watching how they play out on the field is a big part of my time playing. Their placement and speed (APs), movement type (i.e. flying) and what type units you order them to attack also plays a role.

I tend to combine various groups doing various things, and often send commanders in to fight with a few men guarding them and sometimes a magic item and/or mage starting out next to them to cast a spell on them. By placing groups near these groups with orders so they will tend to be fighting nearby... well I've been working on it for years and it takes some fiddling and experimentation and luck and so on, but it's one of the most compelling parts of the game for me.