David wants to time-stamp a custom field called 'MQL DateTime Most Recent' every time a...

To time-stamp a custom field with the current date and time, David would use a System token in the “Change Data Value” flow step. System tokens are tokens that reference system-level information, such as date, time, IP address, etc. The System token for date and time is {{system.dateTime}}. Person/Lead tokens and Trigger tokens are not suitable for this purpose, as they reference person-level information or trigger-specific information.