Yes, there IS a danger and the cost of replacing an cracked engine block is $$OUCH.
My boat is in for maintenance and part of that process is a test drive. The initial work was done weeks ago but the water test drive wasn't done until yesterday because of the risk of freezing or the expense of re-winterizing it after the test.
Why now? Because the 10 day forecast is all above freezing and by the end of the month the average daily low is well above freezing (37). Even the record lows from that point are not a HARD freeze, only 29 or above. The engine block would retain heat and a mild and short duration of freezing air would not be enough to freeze the block.
Also, I suspect the risk is greater for a boat sitting on a trailer (like mine also) than in the water. The lake temperature is around 40. Any boat sitting in it is going to have a hard time getting to freezing. A boat on a trailer is surrounded by the air which if cold enough will cause the boat to freeze as well.
For YOUR situation, if you are parking the boat around the lake or further south you could probably put it in from this point on. If parked further north, maybe soon. Check the weather records for your area. On the other hand, to be perfectly safe and not risk $10,000+ for a engine for your new boat, you might want to wait a couple more weeks and then look at the 10 day forecast for your home.
I'm feeling pretty safe for right here because the marina is quite experienced with this issue and if they are comfortable, so am I. However, I did double check them.
BTW, NOT a stupid question at all.