The easiest thing would be to sort the array in post_randomize()
function void post_randomize()
ts.sort();
endfunction
But if you have other constraints that depend on having the array in the correct order, you will have to put your constraint within the foreach
constraint pyld {
foreach (ts[i]) {
ts[i] inside {[0: 1024]};
i>0 -> ts[i] >ts[i-1];
}