The default date format seem to allow the use of PostgreSQL formatting rules, like datetime_format(field('<your-field>'), '<your-format>'), where <your-format> is anything supported by PostgreSQL, as described here: PostgreSQL TO_CHAR Function By Practical Examples
A problem though, is that it doesn’t support direct conversion to Unix Seconds, useful in many computations. The closest conversion I found, is go by proxy of Julian days (J):
Does the date_diff function solves the issue? I tried the following formula: date_diff(‘ss’, todate(‘1970-01-01’, ‘YYYY-MM-DD’), field(‘Date’))
I simply calculate the difference between start of the unix timestamp (1-1-1970) and the value of the field containing my date. Setting the format to seconds (ss) return the unix timestamp in seconds.