I am still confused.

1.) Ok, if the history tab in Electrum shows the timestamp of the first confirmation:
    Where can I see INSIDE Electrum when I sent initially the transaction to the mempool?
   
    Again: TWO timestamps are required: initial sent (to mempool) and 1st confirmation.
    That should be feasible in Electrum.
   
    I don't need absolute exact timestamps. A timestamp +/- 30 seconds would be acceptable.
   
2.) The blocktime is a timestamp without a reference time zone and therefore useless.
    Its like if I say "I pay you 4000". Pay what? US-Dollar, Euro, Swiss Francs, British Pounds?
   
    A useful timestamp should have a visible associated timezone like "CET" (for Central European time) or PST (Pacific Time Zone)
   
    See here: https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
   
    Or at least an indicator like UTC+-XX See here:
   
    https://en.wikipedia.org/wiki/Time_zone
   
    Usually globally oriented software append this information to each timestamp value.