Creation date of a theme is listed in the “Date Deleted” column from Editor Tools about addons

[wagnerand]

Please refer to https://wiki.mozilla.org/Add-ons/Contribute if this is your first contribution.

Mentor: @eviljeff

If you want to work on this issue and need more information on how or where to fix it, please comment here and we will be happy to provide more details.

[eviljeff]

(copying from irc)
For themes the date deleted column is showing Addon.modified.

The modified date is set on a cron job so it won't be updated until the following day. Some possible fixes are a) change the theme deletion log to use the same source as the addon deletion log (activity log) [hard];
b) set the modified property when we delete the addon, in Addon.delete() [easy].

[ValentinaPC]

Verified as fixed on AMO-dev FF50.1(Win 7).
Postfix screenshots: