Set so that LibreOffice Impress will go straight into show slide mode
You can also do this using terminal
Open terminal Ctrl+Alt+T and run following command
libreoffice --show yourfilename.ppt
I wanted to run a presentation looping on a notice board but for some odd reasons, pps files were inserting a pause of 10 seconds between last and first slides even if I set the relevant option to 0 sec, whereas odp was working fine.