In short, the team plans on sticking with their 12-13 week dev cycle for this expansion. However, the full answer is a bit more complicated than that. They say that they want to release 3.14 in early-mid April about five days after the end of Ritual League.
As expected, the announcement will be streamed on Twitch as with previous announcements. They do note, however, that 3.14 will be smaller in scope than 3.13,
“It's worth noting that the scope of 3.14 is smaller than 3.13, which was itself larger than the average expansion. 3.14 should still include all the normal things you'd expect like a fresh challenge league, balance changes, new items and more.”
They close by expressing their excitement and their desire to create four expansions this year. Meanwhile, catch up on the most recent patch for 3.13.