You did fine! You set an appropriate boundary ("if you are late I will take son to childcare").
Next time don't say anything, just be gone when he gets there. Actions speak louder than words. He saw you ready to leave today. Maybe he'll start to be more on time - if not, you just leave for daycare.
(Be sure to set your departure time to include time to drop son at daycare).
As for the co-parenting communication - set your expectations very low. You can set a good example, but I wouldn't expect much back from him right now. Just document everything, in case he decides later to save money by fighting for 50:50 custody. Some people here have used some software especially for divorced parents to communicate schedules and such - I have no experience with it but others here might advise you, it seems to have been a good way to keep communications neutral.
