Staining / varnishing a door after dip n strip

Dip n Strip implies the franchised non-caustic method, so the doors should not have darkened or be looking too sorry for themselves. If so, just wait till bone dry and then wipe a small area with a wet rag. This is how they'll look with a "clear" varnish. Probably darker than you thought. If they're pine, I wouldn't stain at all, but a light oak shade is fairly safe if you want to even up the colour. IME attempts to make pine look like anything else i.e. darker are doomed to failure.

I'd have asked the people who dipped them, "the drying time" leave them out in the outside for a couple of days and cover with polythene when/if its about to rain.

Best thing after stripping is a good coat of paint. They usually look too tatty for varnish as paint stripping is generally very destructive. The alternative is to do nothing and to live with the now very unfashionable "driftwood" look.

Better to use white spirit than water.