Question: using timelimit in procedures that call procedures

I've made a worksheet (updated)in which I'm timing a program (GTS2) because it sometimes takes a long time to run, and I am not interested in timing the cases where it takes an exceptionally long time to run I've created a timer function that runs GTS2 through timelimit.

timelimit(20, GTS2(H, F, Na, Nd))

this should run the function for 20 seconds, and then stop it if it overruns, before returning that the whole function ( GTS2timer2  ) has taken 20 seconds.

On line 3.3 GTStimer2 is run with two sets of inputs which give a runtime >40s. My guess is that the 20+ extra seconds that the operation takes are spent running solve which is called in GTS, and I expect i can solve the problem by putting solve in the timelimit function directly (if i'm wrong about this please tell my why).

My question is why timelimit isn't able to stop GTS after 20 seconds.

EDIT:

Playing around with the worksheet the morning after I made it the case that was running for 40+s is now giving the error

Error, (in factor/diophant) time expired

My guess is that as it is stopping the solve in GTS2  needs a try/catch of its own. Any idea how to make that work?