933. Ne'ilah

133:23 We are in the practice to put coverings on the floor of the shul because we prostrate ourselves when we recite the order of the Yom Kippur Temple service and we must not do so in a place where the floor is paved with stones. There is something of a prohibition against prostrating even in a place that is not paved, so coverings are placed on the floor. If there are no coverings, it is sufficient to use one's tallis or some other item. (Without something separating one from the floor, one may not extend his arms and legs. If he has nothing to prostrate upon, he may only kneel, or one should lie somewhat on his side - Shaar HaTziyon 131:44.)

133:24 The time of the Ne'ilah service is when the sun is at the top of the trees so that we finish it as (or just before - MB 623:2) the stars come out.  If it continues a little into the night, we still say "seal us" because the attribute of judgment does not depart until the Jews have finished reciting their prayers. However, if the stars have already come out, we do not say "the day is coming to an end..." because that would be inaccurate. Instead, we say "the day has come to an end" and the sun "has come and gone." The shaliach tzibbur says bikas kohanim (the priestly benediction)  and "Sim Shalom" even though it is already night. (While our practice is to say Ne'ilah into the night, one may nevertheless say it while it is still fully day - MB ibid.)