I've done sheet mulched/hugel gardens for many years now with moderate to outstanding success. What I can say is it definitely works. More time before planting into it is better however it seems planting into them right away is usually ok too in my experiences especially with certain species.

Here's some pics of one I planted into right after building it up.

Here's the construction of the mound:

Dug hole
Add tons of logs
Cover with lots of yard brush trimmings
Cover with dirt
Cover with chicken manure
Cover with shavings
Plant!

I like the idea of using hugel mounds for squash vines!  Especially when they're just getting started. It's the first plant that volunteered from the compost buried in my hugel experiment.  And the mound gives more surface area for the vines to roam.

Looks like a well made hugel.  What are you going to plant there?

The top most pic is the completed mound. It has planted in it as of now: watermelon, Seminole pumpkin, pigeon pea, taro, malanga, and yard long beans.