blackshoe, on 2019-January-12, 22:00, said:
Basically, any bid which would be alerted because of its meaning, but which occurs at or after opener's second bid and is above 3NT is delayed.
Suppose the auction goes 1♠-(P)-4♦, where 4♦ is a splinter bid. 4♦ requires an alert because it's artificial. The alert is immediate because it's on the first round of bidding.
Now suppose instead the auction goes 1♣-(P)-1♠-(P)-4♦, where again 4♦ is a splinter. 4♦ requires an alert because it's artificial. However, because it occurs at (or after, in some cases) opener's second call, and is above 3NT, the alert is delayed until the Clarification Period - i.e., after the final pass of the auction.
Alerts for passes, doubles, and redoubles, if required, are always immediate.
Suppose the auction goes 1♠-(P)-4♦, where 4♦ is a splinter bid. 4♦ requires an alert because it's artificial. The alert is immediate because it's on the first round of bidding.
Now suppose instead the auction goes 1♣-(P)-1♠-(P)-4♦, where again 4♦ is a splinter. 4♦ requires an alert because it's artificial. However, because it occurs at (or after, in some cases) opener's second call, and is above 3NT, the alert is delayed until the Clarification Period - i.e., after the final pass of the auction.
Alerts for passes, doubles, and redoubles, if required, are always immediate.
Do delayed alerts work well in practice? In many slam auctions, time runs tight and nearly all the calls above 3NT are artificial: I imagine it might seem a bit dumb to alert them one by one, especially if the opponents are not asking explanations (and if they are, then it might be cleaner and just as fast to ask "please explain the auction").