Leviathan didn't come out until like five or more months after ME3. Inquisition dlc will probably be March or April, maybe later.
I'm looking for news, not a release this very moment.
If the identical release schedule is used as DA2, you would hear about DLC, first week of April, appearing mid-April (with a couple of weeks for holiday season). Mass Effect's dlc took even longer as the Extended Cut (arguably a patch rather than a dlc) got in the way, 6 months post launch.
DAO's 'Return to Ostagar' was quicker at 2 1/2 months, but was arguably a re-skin of the original location with snow.
This is how BioWare do it, and with the positive critical reception, press reception will be warm, and there's an even greater expectation that players will periodically come back to the game.
Not aimed at you, but this forum is very comfortable with shouting both of the following conflicting messages:
- Where's the game / dlc / patch etc - we want it now !!!! and
- It sucks, it was rushed, it was released 'broken'
BioWare should release dlc when they are good and ready - I don't blame them for not talking about it ! 
Legacy was
released about 4 months after launch, not announced. And it was announced and released during a less competitive time. Inquisition has so much AAA competition.
That being said, there is no standard BioWare DLC release schedule so comparing it to previous games is pointless.
And most complaints against BioWare these days are entirely valid. They
do deliver broken games that have to be fixed.