Asked specifically the question what the UA->LH MCT is and was told 90 minutes - I assume the time for UA->LX will be the same. So with undercutting this time checking your bags through is technically not possible...stranger things than a HOT tag have happend, however.

That saids being on two seperate tickets and rules being played after very strictly over here in Europe, I'd say the 65 minutes will be a HIGH risk of you shelling out a substantial amount of money to get to ZRH if you do miss the flight. Things like flat tire rule or rebooking for free because you ask nicely are very unusual occurences, so prepare to upfare you segment to full Y in case you miss you scheduled flight.

So all in all, with two seperate tickets I would give it at least three hours...

Greetings - Dirk