Contemporaneous records are documents created at or close to the time of the events they describe: site diaries, photographs, delivery tickets, meeting minutes, emails and messages sent on the day.
They matter because memory is treated as unreliable and self-serving once a dispute exists. A record made before anyone knew there would be an argument is inherently more credible than a statement drafted after it. Guidance such as the Society of Construction Law Delay and Disruption Protocol repeatedly emphasises the importance of good contemporaneous records to both proving and defending claims.
In practice, the party with the better contemporaneous records usually controls the narrative of a dispute, whatever the underlying merits.
Construction Metric captures records this way by design, filing site WhatsApp messages and photos on the day they are sent: see a sample diary built from them.