Hi,
Currently, there is only one predefined TimeFormat for parsing the option --time in restic, which is not flexible enough in my opinion.
It cannot store nanoseconds, and timezone (currently UTC).
How about trying to parse the time string with a subset of Golang predefined time-format as well as the current one and accepting a reference file?
Thanks.
Can you tell us why you are worried about specifying nanoseconds for your snapshots?
I wouldn’t find it very useful to have nanoseconds as I don’t make snapshots multiple times a second.
You’re right. I don’t find it useful either.
The reason that I want this is just that the repo is able to store nanoseconds, so I want it to store that. 
It’s just a nice to have feature to support other time formats and enhance flexibility and usability.
Supporting a reference file is also an issue of flexibility and usability.
Although we can acquire the required format by date --rfc-3339=seconds -r <filename> to get mtime, and pipe it to cut -d+ -f1 for stripping the timezone, it’s a little bit complicated.
What’s your use case, big picture? Usually, --time is only needed when for example historical data is to be archived, which should have the right timestamp. What are you using it for?
I’m worrying about feature creep: does restic really need this? Or is it just “nice to have”? At the moment, I’m not convinced restic needs this.
The idea is to preserve as more information as possible, no matter it’s useful or not. As the nanoseconds are rarely used, supporting that is merely a nice-to-have.
Then, what about supporting a reference file/directory?
It’ll be useful when the historical data is based on directories/files, and ease the migration process.
Yeah this doesn’t sound like something restic needs to be frank. I just don’t see why anybody would like to see the nanoseconds where it would not benefit nothing restic actually does which is being a backup utility.
I think there are more interesting and pressing features on the horizon that need attention.