Week 3, Trigger Word Detection

I have a question about the week 3, Trigger Word Detection. In the function insert_ones where we want to add labels of 1 to the slices of the data which contain the “activate” word at the time [t, t+50], t being the time activate is spoken, when I try to use the following range, it does not work:
(segment_end_y ,segment_end_y+ 50)
My reasoning to use this range is because if activation word has been said at time segment_end_y, then, according to instructions, we should only consider the time right after it. So, if we use segment_end_y, it will be correct given the way Python starts index from 0.

The code however only passes when I use:
(segment_end_y+1 ,segment_end_y+ 51)

I wonder which one is correct.

Please have another careful look at the instructions. The point is that the start of the insert is +1 from the segment_end_y and then it goes for 50 steps, right?

Thus we have:

start_insert = segment_end_y + 1

What is 50 steps after that?