17. Time, Validation & Assumptions

Time model

• All timestamps are in UTC seconds.
• Device clocks must be reasonably accurate; drift is allowed up to 1 hour between terminal and gate.
• Session windows are bounded on the card and by backend grants.

Validation rules

• Check-in must complete before any terminal operation.
• Check-out should occur within 24 hours.
• Invalid transitions or timestamp inconsistencies are treated as tamper signals.

Assumptions

• Users can carry cards and tap them properly.
• Terminal devices can connect to backend periodically.
• Physical card printing, personalization, and government integrations are out of scope.