Recently someone was asking me this question via e-mail:
"On my home page I have defined a couple of PL/SQL processes that take a long time - like 30 seconds - to finish. These processes fill up some collections that are used on the page to show information. But how can I let the user know that the system is "working", because right now they're watching at an empty screen (or the login screen) for 30 seconds."
Apart from speeding up the queries, there are two approaches to solve this (that I know off) :
An alternative is, to create a "page-in-between". So create a dummy page (like 999). Set the Home URL of the User Interface to that 999 (see pic below). So after login the user is send to that page.
On that page, create Dynamic Action that fires on Page Load, set the Action to "Submit" and in the Settings tab, set Show Processing to Yes - as shown below.
Subsequently, create a Branch to the (slow) Home page. Now, after login the user will see a "Processing bar" until the processes on the home page are finished and the page can be loaded.
For the most APEX Developers, the last alternative will be easier to implement than the one using AJAX calls ....