If you have time-related metadata in your dataset, you can title this column "Date" (no Subset_ required).
Having date information in your spreadsheet may allow you to use the Show Timelines feature in Luminoso. The timeline feature will reveal associations between the topics you create over hours, days, months, or years (depending on the detail and timeframe provided in your data), and will enable you to perform time-based analysis and spot trends over time.
NOTE: The Dynamic Concept Cloud does not contain times or dates (unless these are expressed as random, frequently occurring and important concepts in the natural-language source text).
Our software recognizes most standard date/time formats, including ISO 8601, with the exception of dates written as dd/mm/yyyy, which are standard in the EU.
Your file may even contain date and time information in several different formats, as long as each is a standard format.
Check Data Formatting: General Guidelines for more information.