I've read that 2k primer should set about a week to dry before sanding to allow for shrinkage.I put down three coats of u-tech 2k100 yesterday and I'll give it a week to dry.First question is after I block with 180 would one coat of the 2k100 fill the 180 scratches,I plan on wet sanding with 400.After applying my final coat of primer can I give it a day to dry,wet sand and paint or does the primer need more time to dry?I'll be using spi black bc/cccccc.Thanks in advance for any advice.I really want to get the paint on before it gets too cold.

I use Evercoat Slick Sand and after 6 hrs you can sand away.I use 180 grit dry and then 220 dry 320 dry and 400 dry.I never wet sand primer.You can miss alot of areas buy wet sanding and its a big mess.Dry sanding,you won't miss a thing,you can see it all.The good and the bad.

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Yes allowing a week is a good idea when working with urethanes as they tend shrink. Sand it too soon and the primer will shrink down after you have sanded it thus making it wavy.
No one coat will not likely fill 180 scratches, I would go with another 3 coats. Do your final sanding with atleast 600 grit, IMO 400 is too coarse for basecoat.

Also make sure you give that black basecoat PLENTY of time to flash off between coats as black by nature is a very slow drying base.

I'd second Eric's advice with one difference. I sand with 400, but very lightly. I then will guide coat it and sand with 600 until it is slick with no guide coat left.

Just my own way.

Thanks guys for the input.I did use slick sand and have seen it mentioned that it's better to seal it before paint.I started out with two coats of unreduced epoxy,then I blocked the whole car with 180 and did metal staighten and filler work.Followed that with one coat of epoxy then one coat of slick sand again blocked car with 180.I treated the slick sand like a spot putty basically only leaving what was needed.There was a couple spots that needed some attention for that I used evercoat spotlite glazing putty,then three coats of the 2k100 I put down on Wednesday.I know now is not the time rush but I need to get paint on before it's cold.Is it possible to sand with 180 guidecoat sand with 320 and finally 600 without repriming?Again thanks everyone for the help.

I would do the 220 and 400 step as mentioned above. Preperation is the key. You've come this far, so why skip a couple of steps.

I only finish with 600 when using a metalic base coat. I use 400 on all solid colors. Actually if you are using a generic sandpaper and not true grit sandpaper, 600 would be best for you to use, just to make sure you don't have any sand scratches.