The Files application in Roundcube shows the modified dates of files in the timezone as (note sure which of the two following):
It does not show them in the user's selected timezone, however. This makes the files and other objects such as email appear out of sync in terms of time.
I'm not sure what issue do you have with email, but files are indeed stored with timestamps in UTC. The plugin displays the date as-is provided by chwala. It will be chwala's responsibility to convert it to user timezone (if provided). The timezone would need to be passed by Roundcube to chwala first.
The issue with emails is a user-confusion issue: you get an email with an attachment, you save that attachment "to the cloud", and now the time is oddly different than the email. So it isn't that there is a bug with emails, but that the time differences cause problems for users.
It will be chwala's responsibility to convert it to user timezone (if provided). The timezone would need to be passed by Roundcube to chwala first.
How much of this is already possible? Does this mean that chwala will require some work to be able to accept a TZ, and then the Roundcube plugin would need to be modified to send that TZ? If so, does this mean we should have a ticket open for chwala as well?
Fixed in:
@seigo, do you need this for KE14?