The settings relating to how a slideshow is presented are found on the slideshow settings window. This is displayed by selecting 'Slideshow' from the menu, followed by 'Change slideshow settings' as shown below:
A window similar the that below should now be displayed which is separated into two sections, how the slides change and how the slideshow looks.

Firstly, you can choose how the slides move from one the the next by clicking on the appropriate option. The 'simple change' option makes the slideshow simply stop displaying one phase and start displaying the next. The 'smooth fade' is slightly different. Once the time for displaying one phase is up, it 'fades out' the current phase and 'fades in' the next at the same time. It gives an impression of movement and transition without needing to actually chart the progress and animate the movement between the two phases.
The best idea is to try each option and see which best suits the BattleMap you are creating.
The second item is to choose how long, in seconds, each phase slide is displayed for. This time does not include the fade transition time if that option has been chosen.
There are two options in this section.
Setting the 'do you want the slideshow to fill the screen' option to yes means that the BattleMaps window will automatically expand to fill the computer screen when the slideshow is started, and automatically returns to it's original size when it stops.
Setting the 'do you want it to hide...' option will shrink the tree panel and details panel (as if you had clicked the 'shrink' buttons on the main screen - see items (8) and (10) on the 'main screen layout').
Clicking 'OK' will save these details, clicking 'cancel' returns the details to the state they were in before opening this window.