Couldn’t you just import a text file with the bit sequence of 20 0s and then 10 1s, followed by the remaining number of 0s.The problem with the time delay is that it shifts the entire signal through the time window, but the signal loops through the time window and comes back to the beginning again. So a signal with all 1s shifted in time will still be a signal of 1s.
You could get more complicated and create a bit sequence with 30 1s and then all zeros with a suitable time window and use a time delay on that, but in that case I think using a text file would still be simpler. I made this project in OptiSystem which works except the looping causes an additional peak to form.
Regards