i just configured my first Backup Job, and also recieved the email the Job was completed i noticed that the time stamp is different then the time in the Logs.
the Logs is in CEST for me the right stamp but the other one is in UTC.
If the hardware clock is set to UTC and the Proxmox/Debian timezone to Europe/Amsterdam then the 2 hours difference it to be expected (as @gfngfn256 explained). You can ask Proxmox to use the local timezone in both place (or none of the places) via bugzilla.proxmox.com. Or set the Proxmox/Debian timezone to UTC if you prefer and/or as a work-around.