Why much time is needed to access an applet having swing components the first time?
Wouldn't this vary with each computer or platform? As such the only answer would be to run a test on the platforms you have now.
What do you mean by "first time"? Do you mean
Depending on what you mean it could be that certain components must either be initialized (such as after an install) or loaded into memory (such as after a boot). Some applications like Google Chrome leave threads running in the background after first use (after booting/logging on) in order to speed up loading/running on successive use.
The JRE has a warm up time, yes, its like adiesel engine, powerful but takes time to load every time after rebooting your system.
In addition, an Applet must be downloded (all the .class files of the project) so add this to the loeading time and you will find that Applets are really slow and that's Applets are being abondonned by Oracle (marke as deprecated).
It is because behind each swing part there are several Java objects and resources. This takes time to make them in memory. JDK 1.3 from Sun has some enhancements which can result in quicker execution of Swing applications.