Depends on the math, I suppose. I have no idea what it costs a dealer to keep a car on a lot - probably depends on how much the dealership is leveraged to buy those vehicles, overhead, etc.
Either way, let's take a completely random number and say it costs $600/mo or about $20/day to keep one truck on the lot. Let's say MSRP for that truck is $75k, and they paid $67,500 (10% below MSRP). I have no idea what ADM that dealer is actually adding, but for the example, let's say $20k. Therefore, the dealer has the possibility to make $27,500 + whatever they think they can make by their finance manager selling extended warranty and other BS. Let's call it $30k possible profit from one truck (for easy math). At $20/day, they could let that truck sit for 1500 days and still not take a loss.
You see where I'm going with this? Again, these are completely hypothetical numbers, so that number could be 60 days, it could be 120 days, it could be 280 days.
Edit: Also, it's non-linear right? Meaning they probably do the math and figure out how long they can leave the truck at $20k ADM before they drop it to $10k ADM, then maybe down to $5k, before they finally might let it go for MSRP when the time is right for them. It's not a gamble because they can do the math and figure out when they have to sell at what number to still make a profit (big or small).