We used to have this discussion with umpires when I was the league administrator and we were ASA. Back then there was nothing in the rule book, and they insisted on starting the clock when the home team took the field. If I recall correctly, I found a section in the ASA scorekeeper's guide that said the clock started when the plate umpire called, "Play ball!" Since then the ASA has added the FP rule, but not done anything about the SP rule. I do not know if the scorekeeper's guide has been revised (or, frankly, if my recollection that it was there was correct to begin with).

I do know that we are now NSA and in our league the time starts when the PU says, "Play ball!" The exception is the first game of league-play nights, when the clock starts at 6:30 whether the teams are ready or not.

Also, we did have an umpire call a game one night when we were ASA because, as she said, "No inning starts when there are less than five minutes left on the clock." We later determined that she had learned this from a local military league where that is, in fact, the rule.

Well, that just isn't so. ASA does not differentiate SP from FP.

The time limit issues use to be kept in the code. I guess someone realized that since the umpires are the officials which enforce such rules it should be included in the rule book.