During Shabbat morning davening, we recite Psalm 136 and my siddur has the following instruction, "Most congregations recite the following psalm while standing". So I make sure to stand and then begin to recite it.
However, I am not sure if the practice of standing remains only until I, as an individual, am done saying that section or if I should wait until the person leading the davening says the last line(s) indicating that the congregation as a whole is moving on to the next paragraph of prayer.
In my synagogue I see some people sit down as soon as they are done and wait, while others stay standing and wait to sit until the leader finishes.
Does the obligation to stand end when I finish the last word or when the congregation moves on? Someone davening alone would not have this tension between his private reading speed and the communal progress.
[I know that this same issue arises for other parts of davening so would any answer be local to this prayer, or generalizable to other cases, such as rising for parts of Kabbalat Shabbat?]