What do the numbers written in the top left corner stand for? In The Seven Deadly Sins: The Resurrection of the Command, there is a number which randomly appears in the top left corner, like:


  6:48





  6:49





  6:54




(Image source)

What do the numbers written in the top left corner stand for?
It's the local time in Japan when the show is currently broadcasted. It has nothing to do with anime show.

A thread on MyAnimeList's forum has a quick discussion about this in English.



The official term is 時刻出し (jikoku dashi, time display). As mentioned before, this is not restricted to anime shows, but more to the TV channel and broadcast time. Usually, this occurs for shows in the:


morning: from the earliest show up to 10:00
afternoon: from 11:00 up to 14:00
evening: from 17:00 up to 19:00 (some as early as 13:00)
special occasions: New Year's countdown, on-going sports tournament, momentary announcement (news, earthquake, climate).


The reason for the morning, afternoon, and evening shows are most likely to remind the viewers, such as:


morning: going to work/school before getting late
afternoon: lunch preparation/lunchtime period
evening: dinner preparation




For this specific example of The Seven Deadly Sins: The Resurrection of the Command, the show was broadcasted on local Japanese TV channels (Japanese Wikipedia):


  
  MBC/TBS: January 6 ~, Saturday 6:30-7:00
  Animax: February 18 ~, Sunday 19:30-20:00
  


From the example screenshots of 6:48, 6:49, 6:54, it can be deduced that the scene was taken from MBS/TBS, the earliest broadcast for this series. After knowing the timeslot, it's also possible to estimate the relative timestamp for each scene: around 18, 19, and 24 minutes (next episode's preview) into the show.



References:


Yahoo! Chiebukuro (Japanese)
Yourpedia (Japanese)