Is it bad to cool mash runnings before the boil?

Background:
I brew extremely high gravity (1.120 - 1.140 OG) lagers. I mash 30# of grain to collect 15 gallons of runnings which I then boil down to 6 gallons (twin brew kettle 2.5 hour boil). Getting that and the associated cleanup done (during and after) can make for a very long brew day (10+ hours). The last couple of batches, I split the process over two days by mashing and collecting my runnings on the first day (usually done around noon), then letting the full brew kettles sit over night and starting the boil early (5AM) the next morning. My batches spend 2-3 months in primary before a 10 week diacetyl/secondary/lagering regime, so the lag time between starting a batch and sampling the result can be almost half a year. I'm ready to start another couple of batches, but being a natural worrier, I'm worried that maybe letting the runnings sit over night might introduce undesired results. Before collecting any runnings, I mash out to 190F+ and my grain bed remains above 180F for the entire lauter/sparge. When I turn on the kettles for the boil the next morning, the runnings have cooled to 70F (I live in Alaska). Any other comments regarding my process are greatly appreciated.

During the chill down period, you are definitely susceptible to a wild yeast or lacto false start unless it's covered well. I think the biggest concern is wasted energy. It makes the process take all that much longer as well. I have no idea what you spend on a pound of grain but you might try collecting less wort and shortening your boil. Sure you'll throw away some efficiency, but it will probably only cost 2-3 pounds of grain and when compared to energy costs it may be a wash.

It's not a bad thing, necessarily - but I would be worried about contamination. That sugary wort is a perfect place for wild yeast and bacteria, and if they get in there it could certainly affect the flavor, depending on how much got into the wort.

There's so much stuff floating around in the air that it's inevitable that some makes it into the wort. Probably not enough to affect flavor too much, but still - you never know for sure.

You are probably safe if it's just over night, but I would take serious precautions to keep it covered and safe while it's cooling. It's probably safest if you could stick in the refrigerator if possible, but for sure keep a tight seal on the lids and keep them covered the entire time.

I let a second set of runnings in a boil kettle overnight covered, but outside. I was trying to squeeze out a session brew from a big belgian.
By the next day I had quite a disgusting kettle of very foul smelling baddies. That was the one and only time I tried it. It was during the summer, so it was relatively warm all night, maybe during the winter it would work better?

Why not just use more grain and collect less runnings like Bobby_M mentioned? Seems like a whole lot of work for I'm not sure what. Is there a reason for the 2.5hr boil outside of volume reduction?

Any time you leave your wort sitting, you run the risk of infection. While it's usually ok to leave things sitting overnight, I'd never ever make it an understood rest in your brew day.

your main risk, i believe, is that the wort might sour a bit. wild yeast and bacteria (like lacto) might party in there for 18-24 hours before you boil. they might have an effect on your wort, or they might not. brewers who try to sour their wort, on purpose, add bugs on purpose - and 24 hours is on the low side, most people seem to go longer. they also actively maintain their worts around 100*F, whereas yours will only spend part of the time in the "lacto zone." any bugs or yeast you do pick up will be boiled away so they won't live on to affect the fermentation.

so yes there is a risk, but i think it's pretty minimal if you keep the lid shut and don't toss any raw grains (or other sources of bugs) in there.

Like doc5 said, I sometimes don't clean out my mash tun until the next day. It gets really funking smelling in there! I don't kick up the heat much like you do though, just like 160 or so.

Good luck, but I wouldn't let the wort sit over night.

Grain husks are a hot bed for lacto - without first boiling the runnings you have the perfect environment for it to take off since the mash started...maybe if you cool it fast enough and it stays low enough you'll get by, but as other posters have mentioned, they got the beginnings of a soured mash - summer temps would accelerate that. I second what Bobby suggested; just use more grain to get more concentrated runnings, therefore needing to collect less and boil for less time. Even with a lager and DMS concerns you only need to boil for 60-90 mins.