And everyone liking this idea, please upvote the 3-year old popular idea https://forum.mendix.com/link/ideas/76 of Jelle Dekker.
*More editting: Erika Shakya was able to solve this challenge by using CustomString Widget from the App Store: https://appstore.home.mendix.com/link/app/1426/
We struggled with this as well but we ended up producing a widget to try to solve the problem.
However, adding the delay also caused problems if the page navigation was accessed too quickly as it could end up changing the title on the wrong page. To solve this we had to save the timer handle and if the page was navigated from we had to cancel the timer in the widget.
Another issue was visibility, so we had to check if the widget was actually in a visible block before running. Sometimes we needed it to be conditionally changed. This involved checking the context before setting the timer.
This approach feels really dirty and hacky, but it works for us. Ideally the page title should be easier to change in a Mendix app so it may be worth submitting a request on the Ideas Forum.
This is part of Mendix 8.12
may be for your question this will be useful you can change the title of each page as you wanted in the title section of the page properties.