Consider normalizing the advance notice requirements between the AC meeting and all other kinds of meetings

[hober]

(Split off from https://github.com/w3c/AB-public/issues/283)

How much advance notice is required for all but one meeting type is defined in §3.1.2.1. Meeting Scheduling and Announcements. The one exception is the AC meeting; the advance notice requirements for it are defined in §3.2.4. Advisory Committee Meetings.

We should consider aligning the advance notice requirements. If we're able to fully align them, we could have one set of requirements that apply to all meeting types.

[fantasai]

I think the advance noticed required for larger meetings (like TPAC, AC) needs to be more than for smaller groups, who can be more flexible about timing.