When using dates in FIELDS, you probably either want the date to remain static until you manually update it, or update automatically like other fields. If you use the DATE field name, then the date string will remain static until you manually update it using the UDPATEFIELD command. If you want a FIELD that includes a date that automatically updates, you can use the following DIESEL string in your field.
$(edtime, 0, MON DD"," YYYY-H:MM:SS am/pm)
Here is a reference to "edtime" and all of the other DIESEL functions.
Remember that the value of FIELDEVAL determines what events trigger the automatic field updates. Read more about Using Dates in FIELDS