In reality you are already using a skin, without a skin, almost nothing would work.
In the stock version in the skin there is the essential, in the ux folder you should have about forty zip files, in the file speedcam.zip there is almost nothing, there are no icons and the plugin.ini is empty. The program uses icons that are in the data.zip, plus or minus the iGO Primo icons.
It's true that lately they have filled the skins with superfluous things, but through the skins you can have many more features, those that you do not need simply do not activate them from the menu. In Arimi's latest skins you can also choose whether to use the Minimal version or the Full version.

However to solve the problem without changing skin, try to write the max_section_time line in the sys, you should have the category alarms section at the bottom and add the line like this:

; S P E E D C A M - C A T : 3
[speedcam_category:3]
activated_spoken_type=speech
activated_speech="Average Speed Camera"
max_section_time=100

approach_beep_distances=150
approach_beep_spoken_type=speech
approach_beep_speech="Average Speed Camera"

section_beep_distance=250
section_beep_spoken_type=speech
section_beep_speech="Average Speed Camera"
overspeed_spoken_type=none

overspeed_sound="none"
skin_first_sound="Section_Start"
skin_speed_sound_delay=250
skin_repeat_sound="Section_Start"
skin_repeat_distance=250
skin_off_sound="speedcam_off"

min_frc=-1
use_road_speedlimit=0

100 it's the number of seconds you want to make the average speed control last.

Usually we have to delete the save folder to activate the change to the sys, but I do not know if it is necessary in this case too, otherwise, change it to the plugin.ini which is in the speedcam.zip/ux/speedcam. It should be empty so just write:

[warning]
max_section_time=100

By changing the speedcam.zip file you do not need to delete anything.