I would not do more than one day if you are not freezing them. How you prep it will make all the difference. Sear the beef, chill, pat dry. Seal the inside of the puff pastry with egg wash so you don't get soggy. You need to have control over this process and your circumstances will vary.
I've seared & wrapped my Wellingtons and held them three days once before cooking. It wasn't perfect, and I'd say maybe two days is about all I'd prefer to do. Overnight is no problem. Probably if you tossed 'em in the oven for 3 minutes or so it might help but that's not really the way to do a higher end item like that.