Always line before papering? Drying time of skim coat prior to papering??

Hello

I've been asked to paper following a skim coat. There are different opinions of drying times online. how long would you guys give it?

Also

I was taught it's always best to line before papering and I certainly find it far easier to work with the papers when I do so. I find lining so quick and easy plus most papers advise you line first anyway.
The only time I haven't lined is for very thick papers and I honestly don't think it goes on as well.
Thing is tho, surely a top notch...

Always line before papering? Drying time of skim coat prior to papering??