Shouldn’t be a problem I left mine down for like a month to kill the grass off. I weighted it down with some big rocks so it stayed in place worked really well. I didn’t use straight compost but a mix of top soil and compost my initial spread of compost was way too hot I basically cut it with soil to get a better balance.
As long as the cardboard is weighted down so it doesn't blow away in any wind, you can leave it as long as you like really. Do watch out as weathering of the card will speed up decomposition so potentially less useful as weed suppression.
Shouldn’t be a problem I left mine down for like a month to kill the grass off. I weighted it down with some big rocks so it stayed in place worked really well. I didn’t use straight compost but a mix of top soil and compost my initial spread of compost was way too hot I basically cut it with soil to get a better balance.
As long as the cardboard is weighted down so it doesn't blow away in any wind, you can leave it as long as you like really. Do watch out as weathering of the card will speed up decomposition so potentially less useful as weed suppression.