Here's the review from Mignolaversity on issue two. Scott Allie drops in for a question at the end too:
Scott, to some, Abyss of Time might seem like a random tangent given the conclusion of The Return of the Master, but having read it, it seems pretty apparent that a lot of the threads involved with AoT are going to be important going forward in the series and in others like Abe Sapien even. For those that read Abyss of Time and wonder why now for this story, what do you have to say? Why now for this story in particular?
Scott Allie: The story connects deeply to a lot of things that are going. People felt like it was coming out of nowhere because they were looking in one direction—backward. It felt like a real detour after Return of the Master. But Return of the Master was a big turning point leading to bigger things. Threads that go really far back are starting to come together. Most readers have already figured out the connection between Abyss of Time and Hellboy in Hell, but there’s more to come.
I feel a bit dumb, because I haven't figured it out...