To cut off single product prices for a specific time period is easier than you think:
Click to "marketing"
Enter the -% amount of saving under "highlight"
Fill in Dates under "valid from" and "valid to" (Tipp: If you want to reduce a product Price for an unknown period of time [which is legally not allowed] you can just fill in a date that is in distance
Fill in the real original Price. Your core customers will find out if you lie to them
At "original price description" enter the reason of the reduction (e.g. black friday or summer sale). This is mandatory in Germany.