Hi @jthi,
Your suggestion is indeed what recommended me Ryan Lekivetz in our private discussion ; what he suggests was the introduction of Tick Seconds() function in the design script before and after design generation, to count design generation time
An example below (inspired from Use Matrices) :
t1 = Tick Seconds();
DOE(
Space Filling Design,
{Add Response( Maximize, "Y", ., ., . ),
Add Factor( Continuous, -1, 1, "X1", 0 ),
Add Factor( Continuous, -1, 1, "X2", 0 ),
Add Factor( Continuous, -1, 1, "X3", 0 ),
Add Factor( Continuous, -1, 1, "X4", 0 ),
Add Factor( Continuous, -1, 1, "X5", 0 ),
Add Factor( Continuous, -1, 1, "X6", 0 ),
Add Factor( Continuous, -1, 1, "X7", 0 ),
Add Factor( Continuous, -1, 1, "X8", 0 ),
Add Factor( Continuous, -1, 1, "X9", 0 ), Set Random Seed( 830486233 ),
FFF Optimality Criterion( MaxPro ),
Space Filling Design Type( Fast Flexible Filling, 27 ), Simulate Responses( 0 ),
Set Run Order( Randomize ), Make Table}
);
t2 = Tick Seconds();
Show( t2 - t1 );
And for this design generation, I can find the value in the log :
t2 - t1 = 2.31666666665114;
So I will use this method manually for my different designs (it shouldn't take too long), if you have any idea on how to automatize this process or make it more simple, you're welcome 
Thanks for the interest and recommendation,
If you are going to do the DoE with JSL, something like this is what I would do. If you have to do them multiple times with different seeds/settings you could go slightly deeper with the JSL.
Names Default To Here(1);
record_doe = function({doe_expr}, {Default Local},
wait(0);
start = Tick Seconds();
d = Eval(doe_expr);
dt = d << Make Table;
wait(0);
end = Tick Seconds();
d << Close Window;
Close(dt, no save);
return(end - start);
);
designs = Associative Array();
designs["Space Filling MaxPro"] = Expr(DOE(
Space Filling Design,
{Add Response( Maximize, "Y", ., ., . ),
Add Factor( Continuous, -1, 1, "X1", 0 ),
Add Factor( Continuous, -1, 1, "X2", 0 ),
Add Factor( Continuous, -1, 1, "X3", 0 ),
Add Factor( Continuous, -1, 1, "X4", 0 ),
Add Factor( Continuous, -1, 1, "X5", 0 ),
Add Factor( Continuous, -1, 1, "X6", 0 ),
Add Factor( Continuous, -1, 1, "X7", 0 ),
Add Factor( Continuous, -1, 1, "X8", 0 ),
Add Factor( Continuous, -1, 1, "X9", 0 ), Set Random Seed( 830486233 ),
FFF Optimality Criterion( MaxPro ),
Space Filling Design Type( Fast Flexible Filling, 27 ), Simulate Responses( 0 ),
Set Run Order( Randomize )}
));
designs["Space Filling Centroid"] = Expr(DOE(
Space Filling Design,
{Add Response( Maximize, "Y", ., ., . ),
Add Factor( Continuous, -1, 1, "X1", 0 ),
Add Factor( Continuous, -1, 1, "X2", 0 ),
Add Factor( Continuous, -1, 1, "X3", 0 ),
Add Factor( Continuous, -1, 1, "X4", 0 ),
Add Factor( Continuous, -1, 1, "X5", 0 ),
Add Factor( Continuous, -1, 1, "X6", 0 ),
Add Factor( Continuous, -1, 1, "X7", 0 ),
Add Factor( Continuous, -1, 1, "X8", 0 ),
Add Factor( Continuous, -1, 1, "X9", 0 ), Set Random Seed( 1 ),
FFF Optimality Criterion( Centroid ),
Space Filling Design Type( Fast Flexible Filling, 20 ), Simulate Responses( 0 ),
Set Run Order( Randomize )}
));
design_durations = Associative Array();
For Each({{design_name, design_expr}}, designs,
design_dur = record_doe(design_expr);
design_durations[design_name] = design_dur
);
Show(design_durations);
You could also of course save the designs</CODE></P></LINGO-BODY><LINGO-SUB id="lingo-sub-897331" slang="en-US" mode="CREATE">Re: How to record DoE generation time ?</LINGO-SUB><LINGO-BODY id="lingo-body-897331" slang="en-US" mode="CREATE"><P>Thanks a lot for the solution <A href="https://community.jmp.com/t5/user/viewprofilepage/user-id/14366" target="_blank">@jthi</A> !<BR />The script sounds good for automating this to few designs, but since I have to run it for 31 designs, it would be a little tedious to add each DOE generation script inside the array. I will continue with the "manual" version, with the upgrade mentioned by <A href="https://community.jmp.com/t5/user/viewprofilepage/user-id/5358" target="_blank">@Mark_Bailey</A> to replace Tick Seconds() by HP Time(), as it provides a more precise measurement in microseconds.<BR />The final script for one specific example looks like :</P>
<PRE><CODE class=" language-jsl">t1 = HP Time();
DOE(
Space Filling Design,
{Add Response( Maximize, "Y", ., ., . ),
Add Factor( Continuous, -1, 1, "X1", 0 ),
Add Factor( Continuous, -1, 1, "X2", 0 ),
Add Factor( Continuous, -1, 1, "X3", 0 ),
Add Factor( Continuous, -1, 1, "X4", 0 ),
Add Factor( Continuous, -1, 1, "X5", 0 ),
Add Factor( Continuous, -1, 1, "X6", 0 ),
Add Factor( Continuous, -1, 1, "X7", 0 ),
Add Factor( Continuous, -1, 1, "X8", 0 ),
Add Factor( Continuous, -1, 1, "X9", 0 ), Set Random Seed( 830486233 ),
FFF Optimality Criterion( MaxPro ),
Space Filling Design Type( Fast Flexible Filling, 27 ), Simulate Responses( 0 ),
Set Run Order( Randomize ), Make Table}
);
t2 = HP Time();
Show( t2 - t1 );
Thank you all for the valuable inputs !