Top Dress Mix For No-till Living Soil 1lb.

Top dress just turned to cement on top of the mulch. Pretty hard to break through it, I can't imagine seedlings having an easier time. How long does it take to reach the soil and thus become available for the plants?

Every setup is different. If you have so much mulch, and have added so much top dress that it has created a hardened layer on top of the mulch, then I would suggest to move your mulch next time, and add the top dress, then put the mulch layer back in place. That way the worms, and insects can then work on the top dress mix that is sandwhiched between the soil layer and mulch layer.

How many cu ft of soil will 1lb of amendments cover

Here is a base suggested use rate for the amendment blend 

15 gallons 1/2 to 1 cup
30 gallons 2 to 3 cups
50 gallons 5 to 6 cups 
4 x4 soil bed 12 to 15 cups

I see that it says to reamend soil between cycles, does this mean for the first time using redbud living soil you dont need this?

When using the soil for the first time, there are plenty of nutrients in the soil to complete an entire first grow. No need to top dress anything. Once you finish your first grow and harvest, you should top dress our premixed amendment blend.