When's the next time we expect B.Hector?

In all reality: No way to know.

At the very least I don't expect him on a legendary banner any time soon.

Maybe on a wave themed banner?

because of how good B!hector is, he's probably gonna be coming back on march or april on a skill banner.

Well if we look at the first Brave Heroes history:
Roy has only 4 appearances (so many reds)
Lucina has 6
And both Lyn and Ike have 8
That's since #49 - Now we're at #185.

The original brave's had a tempest trial at #72. 23 banners later, There are more banners nowadays but but that could still very realistically be this month or next to time with the hype around 3.0 (and Christmas pocket money).

Also Lucy as the blue has never actually been on a skill banner and still managed 6 appearances.

I can see a future VG about Odds and Evens when they manage to give Even Attack and Odd Defense to non exclusives so that's potentially one.

Another would be heroes with Ignis.

If he's the first to reappear out of the 4 of them it's probably a good sign he'll be around every few months at least.