Bcuzz atami soil a&b

I got these Bcuzz soil A & B for free and my plan is to use them with my plants (don't have any others, but bloom&topmax)..

So now i'm wondering: Do i really have to use them at the same time?
I mean, so i can't start only with Bcuzz A, and give Bcuzz B much later?

Thnx for the help.

Plants:

I guess I just can't use any other fertilizers at the same time when I use "A and/or B".....