Current AIP ENR 1.10-16
AIP Time of Departure; Requirements states:
“ETSs more than 7 days in advance at the time of notification cannot be accepted”
Yes sports fans, you can submit now up to 7 days in advance and have been able to do so for years.
ICAO doc. 4444 amendment 1
ICAO 4444 amd 1 says "4.4.2.1.1 Flight plans shall not be submitted more than 120 hours before the estimated off-block
time of a flight."