Decoupage help - curing time

[OUB1974]

I'm making a Christmas box, which I've varnished and have a picture to stick to it. I was planning on using mod podge, but I've just read the instructions and it takes 4 weeks to cure - I have to post it next week!

The picture is painted with acrylics on paper. Does anyone have any tips on how to stick it on please? Do I need to seal it?

I use authentico decoupage medium and it hardens quickly. But diluted pva often works well. I would try on something that doesn’t matter first to check it will stick and colours won’t run.