Sunday.... used to be very predictable that server connection issues happened on Sundays. I have been in the game today and had no issues although I did notice occasional stutters when carrying out engineering modification "rolls". So just persevere, it is OK from the UK at the moment (just checked again).
EDIT - the launcher message never seems to indicate issues when servers are busy, just when there is a more serious issue of connectivity - well that is the impression I get.