It’s the Page Down button he’s using. Not the down arrow. For each Page Down, it advances the playhead 1 second from the left marker. No, you don’t have to use Page Down. Just reposition it manually if you would like.
The Text filter does not yet have keyframes, but it has filter trimming as shown in the video - all filters except fades support trimming.
In any case, you need to more clearly state the problem, which you did not do at all - not even close.
You have been repeatedly posting without any useful information. Do better, please, or I must silence you in the forum for a while.