By the time the IESG schedules the vote, ADs need to already have educated themselves about the document.
Oh, so you're suggesting adding another phase to the process: IESG education. OK.
So here's a simple proposal that pays attention to AD workload and includes a simple efficiency hack:
When the IETF Last Call is issued, wait a few days, to see whether any serious issues are raised by the community. The really serious ones usually are raised quickly. If there are none, it's pretty certain the document will advance to an IESG vote. That leaves 7-10 days of IETF Last Call for ADs to get educated and ask questions, just like everyone else.
Placing a time limit on some phase of the process doesn't produce quality. The process should take as long as it must in order to produce a good outcome. The question shouldn't be how long the process takes (that's just a cheap shortcut), it should be how to make it more efficient in doing well. I have an idea: let's place a time limit on working groups: they need to finish drafts in six weeks or there will be penalties. Why not?
Scott