This thread appeared in the Google Maps Troubleshooting Group in which Maps Guide Jen confirmed that there is a 5 edit limit to the number of Maps edits that can be made at one time:

TOPIC: Editing limits
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== 1 of 3 ==
Date: Wed, Mar 19 2008 2:04 pm
From: keithdtyler@gmail.com I’m going around my town, looking up places I know of, especially
fairly newly opened places, and updating them in Google Maps.

But after every 5 edits or so, I get a message saying “You’ve edited
too much lately, come back later.”

This is dumb. I’m actively trying to go around my town fixing places,
and I don’t see the point in doing 5 now, then having to wait an hour,
do 5 more, wait another hour, 5 more, etc. I’ll just stop doing it,
because it’s not worth the insulting annoyance.

== 2 of 3 ==
Date: Wed, Mar 19 2008 2:12 pm
From: NWT

Actually, I think it’s great. Google wants to prevent people from
abusing the system. They don’t know if what you are doing is true or
not, so they limit the number of times you can do it.

If you understand, that’s fine. If you want to be insulted by it,
that’s fine too. But, then, how do you propose they prevent abuse?

== 3 of 3 ==
Date: Wed, Mar 19 2008 3:33 pm
From: “Maps Guide Jen”

Nobody likes spam (unless it’s spiced ham, in which case I’m all for it),
but we’re definitely not out to frustrate you and prevent you from using
this feature, either. I’m making a note of your request. Thanks for your
feedback, and thanks as always, NWT, for your insights!

-Jen