How to programmatically use Workflow module

Sorry if this has been explained else where, I might have missed it. And I have been reading a lot.
I'm using workflow 7.2.x-dev with workflow_field module to add a workflow to an entity.

I am a bit confused at the moment on the best way to programmatically change a state with the new (for me anyway) OOP way of dealing with workflow.

1. Can somebody please give me an easy example to programmatically change a workflow state. I am also especially interested setting up a new scheduled transition. Basically:
if user change state from A->B, I want to automatically set up a scheduled change to change to C at time x

I know there is Rules module, but I would prefer to use code, as there are some other things I want to do.

2. I take it, to detect a state change, the best is still to use hook_workflow with $op transition_pre? Or is there a better way?