The program goes to print Friday. You still need a yes on a Thursday 2pm slot from a speaker who has been in three email chains with three organizers. Each chain has a different room. None of them has the recording policy in the same place.
A speaker is not on your planning committee. They will not reconstruct the grid. They will answer a closed question with a clock time, or they will wait, which is how you go to print with a placeholder.
The slot is usually the first ask
"Can you take Thursday 2:00–2:45pm in Room B, forty minutes plus questions, session recorded, yes or no, by Tuesday 5pm your time." That is a decision. Travel, hotel, and whether they want a rehearsal are later letters.
If the real blocker is a flight, say that, and ask only the flight question. Do not hide a travel no inside a cheerful slot confirmation.
Give the facts a cold speaker needs: city, venue name, day, clock time in a named timezone, talk length, recording, and who meets them at the room. Cut the recap of how the program committee argued about tracks.
Your lean: "We are holding 2pm. If that is impossible we can do Friday 10am, and I need that no by Tuesday." Two options is still a closed list. A menu of six slots is homework.
An honest deadline, in their clock
A decorative ASAP trains the next speaker to ignore you. Name the date the program locks, in their timezone, and what you do if they do not answer. "If I do not hear by Tuesday 5pm Pacific, I release 2pm and write you the Friday option once."
Organizers forget that "end of day" is meaningless across a continent. Write a clock time and a zone.
They may have no account. Write anyway. The mail is the product. They reply from the mail or the page. You approve the wording. The assistant does not confirm speakers as you.
If you live in Claude and they live in ChatGPT, the briefing is what crosses. Their notes do not.
No handbook file. Write the five facts. If a page already holds the rest, name the page.
What a sufficient reply is
"Yes." "No, I can do Friday 10." "Yes if it is not recorded." One line. Say that is enough. A speaker who wants to change the title can do that in a second exchange after the slot is held.
Do not put a private nickname in the package. Use the name on the talk.
One speaker per send. A speaker list is not a recipient list. Forty speakers is forty approvals. That is slower than a mail merge and it is why a merge reads as spam.
What this is not
It is not the talk. If you need an abstract rewrite, that is a review of a draft they already wrote — a different shape, and it needs the draft in the note, not a file.
It is not a place to renegotiate the whole program. One slot. If the track is in trouble, that is a conversation among organizers first.
If your assistant already has the grid, let it draft the one-slot package. You read the times. Then they can answer without opening three chains.