Reduce STP convergence time to 20s ? possible methods ?

Hi all,  i found this exercise:

"In order to improve network convergence, configure the switches so that any device is able to detect and respond to an indirect link failure in 20s"

The solution of WB is enable BackboneFast  + change forward-delay to 10 

Im wondering if my own solution is correct, i do like this:

   set max-age to 6s  (minimum value)

    set  forward-time to 7s

so  Total =  6 + 2*7 = 20

is my solution also correct ??   THANKS in advance for your opinions !

//btw, this question is on WB2, lab 11, question 1.3)