Epoch Time, now, in Webhook

Hi All -- I've tried looking into some scripting to do this, but it's a bit out of my wheelhouse. I'm basically looking to timestamp a webhook. Using JSON payload is there a formula to calculate the current Epoch time (minus 7 hours if possible, to be in PT).

My trimmed down payload should be something like this (which works -- I'd just rather it be a token or script or embedded function instead of the static #)

payload={ "attachments": [ { "ts": 1506456000 } ] }

note: I can use this as a my.token if needed -- I already have a workaround for that.