Cover cropping oats in sheet mulch

This year I'm starting a garden bed in a weedy urban backyard. There used to be a garden plot in the back a few years ago, but it got filled in with various grasses and pioneer plants due to neglect - not to mention a boatload of mint! It's a semi-shaded area but still gets plenty of sun through the day, and I find the few plants I've stuck back there need little to no watering.

The plan is to lay down a bunch of cardboard boxes as our first layer to smother the existing plants, then add a layer of mushroom compost, sow a crop of oats, and mulch it all with straw (much easier to transport than wood chips). I also want to inoculate a little wine cap bed in the spring toward the back of the garden by a Mulberry tree.

My question is this - my seeds won't be arriving until three days after we're able to lay down cardboard and the layer of mushroom compost. Is it a bad idea to leave the cardboard and compost without a straw layer for a few days to a week? If yes, will the oats still germinate under/in a thick layer of straw mulch? I'd appreciate if anyone who has experience sowing cover crops directly into their sheet mulch might be able to give advice about the best order of operations here.

My partner and I tried a cover crop directly in the soil here this summer after pulling some weeds and had limited success - I'm not sure if it's because we didn't have enough seeds, or if we were trying to grow them with too much straw layered on overtop, or a combination of factors ( I know the birds eating all the sunflower seeds was one, lol).

I know it's a newbie question but any insight would be appreciated!

Thanks!

I regularly sow oats, have never tried it on top of cardboard though. if you are putting down enough mushroom compost (at least an inch) i don't see why they wouldn't.
I have had variable success in germination depending on heat when sowing the oats-- I generally only put down straw or hay to make it more difficult for the birds to get the seeds (and don't worry, the birds got ALL my sunflowers but one last time too).

Oats should be fine on top of cardboard if you're just using them as a cover crop.

The robins eat my oats every year, but I grow rye all the time. I haven't pushed it too far, but thick mulch over the seeds will definitely inhibit growth. A couple inches is probably fine. After that it might start getting iffy.

Thanks for the input! I have sheet mulched one half of the garden - we have to go out and pick up more compost because boy does this use a lot! The farmer I bought my straw from uses similar principles and he was saying not to overthink it - sowing a cover crop might not be a necessary step if I'm just working in my backyard, and the thick mulch should be a useful enough layer on its own. At the end of next year's growing season I'll try sowing the oat seeds to replenish the top layer of mulch for the spring.

Plant the oats. You need a growing root in your compost layer to keep the soil iife going, and to sequester nitrogen so it doesn't wash away, and to grow your own mulch so you don't have to always truck in straw.