When does the 100 night trial start? September 19, 2018 13:36 Updated Follow Don't worry if you need to delay the delivery, the 100 nights start on the day you've received your mattress. Related articles How does the 100 night trial work? Do I have to pay to trial the mattress? What does the mattress 10 year guarantee cover? Do I need a receipt during the guarantee? What size packaging does it come in and how heavy is the box?