Not the answer you want to hear, but some background info:
The 'open form' action is only triggered clientside after the entire microflow has completed. This is because the open form feedback is sent along with the result of the microflow execution. That's why you don't see the form opening immediately after that activity, but only after you press continue (and thus, after the completion of the microflow)
So you want to do some microflow actions after the modal pop-up is shown? Why don't you replace those actions in another microflow which you can trigger in the modal popup with a custom save button or something like that.
Why do you want to wait in the first place?
I think you're going to have to split this microflow into:
1) A microflow that ends with showing the form, and 2) A microflow that is triggered when you save or close that form
Microflows don't stop until they reach an end event (or encounter an error).
You cannot wait for some user interaction within one microflow, so you'll have to create two microflows as Samet and Querijn are suggesting. See also this question for an explanation how (and why) the interaction between microflows and forms works.
Thanks, I've tried my own version of a custom save button, but I am open to suggestions on how to do a proper custom save button.
The reason why I want the microflow to continue after the form closes, is because there are events that trigger before commit that I need to check after commit.
I think it would be a cool feature to have the option to change standard buttons to microflows so you can customize them. So right button on the standard save button and the option change to custom microflow. Helps the new users a lot I think.