No. Someone who can hold a wall sit for 30 seconds is hardly in "top shape." The recommended ability to start the P90X workout program is at least 1 minute (and that is considered a bare minimum to be able to do the workouts), and my 54 year old mom did that on the first try.
If you are having a hard time with 30 seconds, I recommend scaling down the time, but working your way up as you get better. You can safely get out of the position by letting your butt go down to the ground, put a pillow/cushion underneath you if you are worried.
P.S. As a military academy graduate I can tell you that 30 seconds is chump change; 5+ minutes gets you into "top shape" territory where people are collapsing, and pretty much any freshman at West Point, Annapolis, or the AFA can do 3+ minutes.
If you are having a hard time with 30 seconds, I recommend scaling down the time, but working your way up as you get better. You can safely get out of the position by letting your butt go down to the ground, put a pillow/cushion underneath you if you are worried.
P.S. As a military academy graduate I can tell you that 30 seconds is chump change; 5+ minutes gets you into "top shape" territory where people are collapsing, and pretty much any freshman at West Point, Annapolis, or the AFA can do 3+ minutes.