How can I fix the duration of each slide ?

There is no such setting available directly within the plugin. However, you can make a modification in the Widget.Slider plugin.

To do this, please navigate to the following file:
src/Plugins/Widgets.Slider/Views/Shared/Components/WidgetSlider/Default.cshtml

Once there, locate line 5, which reads :interval="6000". You can replace this with your desired value.

For additional parameters available for the slider, please refer to the Bootstrap Vue documentation here: https://bootstrap-vue.org/docs/components/carousel

After making the necessary changes in the plugin source, you will need to rebuild the plugin and upload it to the server.