@Les12706
First, it would depend on whatever your contract states regarding terminating your agreement with the property management company.
Terminating a property managed listing happens all the time and I have never heard of Airbnb doing this. The previous property manager should just block any dates on their calendar past 4/30 and/or unlist now. They can communicate with any current guests while "unlisted" it just means no furture guests can see or book the listing. Eventually the propery management company should permanently remove the listing they are managing.
BTW....never allow a property management company to be named as "owner" as all the reviews will stay with them if your agreement is terminated...you will have to start over. They should be named as Co Host and if they refuse, move on. Use an experienced Co Host instead.
You should be able to publish your listing whenever you want, but you should block your calendar so as not to accept any bookings on your new listing before 4/30.
This could possibly be due to Airbnb's duplicate listing policies, but have never heard them block the Owner's new listing before.