If this is the mattress shop, the guidelines say "Listen carefully, engage in the conversation with the Associate, and take your time. A good sales presentation can take approximately 30 minutes and you should not rush the Associate. " It does not state a minimum time required to be in the store, and I think they are just checking to be sure you did not rush the associate.
This is similar to their drive-in fast food shop, where the reimbursement is less than $8 but the allowable items frequently run more. When you spend more than $8, the report has a popup question "Why did you spend more than $8?" I just say what I had (which are items listed on the allowable list) and I never hear any more.