The documentation states that EPOCH(..) and EXTRACT(EPOCH FROM ..) return double. I should be able to perform calculations on those. For example, I should be able to find the number of seconds since the epoch with

SELECT EPOCH(NOW()) / 1000;

However, this query produces the error

TEIID30070 The function '(EPOCH(NOW()) / 1000)' is a valid function form, but the arguments do not match a known type signature and cannot be converted using implicit type conversions.