If I'm short on time when varnishing I will recoat just after the previous coat of varnish has lost its tack. I have found it very difficult to see where I have applied my new coat over the old which usually results in holidays. If you have good lighting go for it. If I miss that time I will wait 24 hrs. then sand. I'm in Louisiana and to my memory I have never had the privilage of varnishing under proper conditions so I must wait the 24 hrs. to ensure dryness.

I do try to sand between coats as standard practice. I find my final finish is better when I do. Since your in a hurry, I would sand as lightly as possible so the coats will build quickly if you do sand.

Varnishing is a huge subject, I hope you get more opinions which differ from mine. I would like to read them as well. Good luck.