How dry does linseed oil have to be in order to varnish?

[mayday]

I applied the linseed oil mix three weeks ago inside and out to my '55 Otca. It seems to be dry for the most part except for just a few spots here and there. Does the interior appliation need to be perfectly dry to apply varnish or do I need to wait longer?

Which varnish is best...and yes I do plan to sand between coats!

Jeff