You can still avoid most of the effects of a worst-case bias by adding two additional measurements.
Rather than 1 person, 30 minutes (one measurement), given 3 who all had the same experience, you are less likely to have all three have an impression unconnected with the substance of the conversation.
Rather than 1 person, 30 minutes (one measurement), given 3 who all had the same experience, you are less likely to have all three have an impression unconnected with the substance of the conversation.