As it is written, the parallel pool will start when the parfor is called, which is then included in the timing. And since you're not explicitly starting it, it could be starting as many as 12 workers. Try the following:
clear all
% Time how long it takes to start the pool
tic
parpool(5);
toc
% Time how long it takes to run the parfor
tic
parfor i = 1:5
fprintf('Progress %d of %d...\n',i,5);
pause(5);
end
toc
To make this a bit more robust, query Slurm for the number of assigned tasks to start your pool (doing this off the top of my head, I think it's SLURM_NTASKS).
sz = getenv('SLURM_NTASKS');
if isempty(sz)
% For some reason, we're not running in a Slurm job
sz = maxNumCompThreads;
end
% Time how long it takes to start the pool
tic
parpool(sz-1);
toc
% Time how long it takes to run the parfor
tic
parfor i = 1:5
fprintf('Progress %d of %d...\n',i,5);
pause(5);
end
toc
Lastly, since R2019a, you can shorten
matlab -nosplash -nodesktop -r "PCTest; exit"
to
matlab -batch PCTest
