submit_time as shortcode in Contact Form 7 email

Hello,
using the great Contact Form 7 ( Version 4.0.1 ) plugin, I need to add in the SUBJECT of automatically sent EMAIL a “unique-id” like float Unix timestamp with microseconds.
I think [submit_time] shortcode is only present in DB extension (a great couple)
All my attempts to format the fields [_DATE][_TIME] like using [_format_{field} "YYYY-MM-DDThh:mm:ss.ssss"] did not work.

Do we can use the submit_time as shortcode?,
or an alternative method?
REMEMBER is in CF7 Emails , not in DB extension