The Wards I've been in, past and present, always seem to make it a point to have someone ring the hallway bell five minutes before the end of Sunday School and then again when it should be over.
I've never understood why two similar bells rung at the end of block time (for wards who have Sacrament meeting first) don't exist. That's at the end of Priesthood, Relief Society and Primary.
So, when I was a substitute bell ringer the other week, I decided my new unofficial calling is to ring the bells at the end of block, if only to be consistent, and help ensure the block time ends properly on time.
Of course, if I have to substitute teach High Priest group again (or say a closing prayer), that may not happen, but otherwise, it is my new goal.
--In a related concern, my chapel lacks a block on its west wall. There is a clock on its east wall, but that's only visible to those on the stand, or those who sit on the west side of the chapel.
I think this is also an inconsistent practice, that makes no sense.
And, at a recent fast and testimony meeting, I spotted a mother and daughter get halfway toward the podium from the back overflow, only to see the bishopric close the meeting. Those two were sitting on the east side of the overflow, where the lone clock is NOT visible on the east wall.