I'm not going to adjust my schedule for my ex
Why don't you want to adjust your schedule for them?
I simply don't like doing things her way.
It's understandable to not feel like you have to do what someone else wants you to just because you have a prior relationship with them. You should try to avoid making a big deal about it though to avoid having it blow up into something more than it is.
I already plan on being late, I want her to be inconvenienced too.
While most people end their relationship and break off contact. If you did make plans with her together should you not try to be there on time? Technically you could have said no to the meeting to begin with.